feat: add dashboard aggregation endpoint (Phase 2I)

GET /api/dashboard returns aggregated data:
- deadline_summary: overdue, due this/next week, ok counts
- case_summary: active, new this month, closed counts
- upcoming_deadlines: next 7 days with case info
- upcoming_appointments: next 7 days
- recent_activity: last 10 case events

Uses efficient CTE query for summaries. Also fixes duplicate
writeJSON/writeError declarations in appointments handler.

backend/internal/handlers/appointments.go

@@ -203,14 +203,3 @@ func (h *AppointmentHandler) Delete(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusNoContent)
 }
 
-func writeJSON(w http.ResponseWriter, status int, v any) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(v)
-}
-
-func writeError(w http.ResponseWriter, status int, msg string) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(map[string]string{"error": msg})
-}

backend/internal/handlers/dashboard.go

@@ -0,0 +1,32 @@
+package handlers
+
+import (
+	"net/http"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+type DashboardHandler struct {
+	svc *services.DashboardService
+}
+
+func NewDashboardHandler(svc *services.DashboardService) *DashboardHandler {
+	return &DashboardHandler{svc: svc}
+}
+
+func (h *DashboardHandler) Get(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	data, err := h.svc.Get(r.Context(), tenantID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusOK, data)
+}

backend/internal/router/router.go

@@ -27,6 +27,8 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	// Middleware
 	tenantResolver := auth.NewTenantResolver(tenantSvc)
 
+	dashboardSvc := services.NewDashboardService(db)
+
 	// Handlers
 	tenantH := handlers.NewTenantHandler(tenantSvc)
 	caseH := handlers.NewCaseHandler(caseSvc)
@@ -35,6 +37,7 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	deadlineH := handlers.NewDeadlineHandlers(deadlineSvc, db)
 	ruleH := handlers.NewDeadlineRuleHandlers(deadlineRuleSvc)
 	calcH := handlers.NewCalculateHandlers(calculator, deadlineRuleSvc)
+	dashboardH := handlers.NewDashboardHandler(dashboardSvc)
 
 	// Public routes
 	mux.HandleFunc("GET /health", handleHealth(db))
@@ -86,6 +89,9 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	scoped.HandleFunc("PUT /api/appointments/{id}", apptH.Update)
 	scoped.HandleFunc("DELETE /api/appointments/{id}", apptH.Delete)
 
+	// Dashboard
+	scoped.HandleFunc("GET /api/dashboard", dashboardH.Get)
+
 	// Placeholder routes for future phases
 	scoped.HandleFunc("GET /api/documents", placeholder("documents"))
 

backend/internal/services/dashboard_service.go

@@ -0,0 +1,151 @@
+package services
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+)
+
+type DashboardService struct {
+	db *sqlx.DB
+}
+
+func NewDashboardService(db *sqlx.DB) *DashboardService {
+	return &DashboardService{db: db}
+}
+
+type DashboardData struct {
+	DeadlineSummary      DeadlineSummary       `json:"deadline_summary"`
+	CaseSummary          CaseSummary           `json:"case_summary"`
+	UpcomingDeadlines    []UpcomingDeadline    `json:"upcoming_deadlines"`
+	UpcomingAppointments []UpcomingAppointment `json:"upcoming_appointments"`
+	RecentActivity       []RecentActivity      `json:"recent_activity"`
+}
+
+type DeadlineSummary struct {
+	OverdueCount int `json:"overdue_count" db:"overdue_count"`
+	DueThisWeek  int `json:"due_this_week" db:"due_this_week"`
+	DueNextWeek  int `json:"due_next_week" db:"due_next_week"`
+	OKCount      int `json:"ok_count" db:"ok_count"`
+}
+
+type CaseSummary struct {
+	ActiveCount  int `json:"active_count" db:"active_count"`
+	NewThisMonth int `json:"new_this_month" db:"new_this_month"`
+	ClosedCount  int `json:"closed_count" db:"closed_count"`
+}
+
+type UpcomingDeadline struct {
+	ID         uuid.UUID `json:"id" db:"id"`
+	Title      string    `json:"title" db:"title"`
+	DueDate    string    `json:"due_date" db:"due_date"`
+	CaseNumber string    `json:"case_number" db:"case_number"`
+	CaseTitle  string    `json:"case_title" db:"case_title"`
+	Status     string    `json:"status" db:"status"`
+}
+
+type UpcomingAppointment struct {
+	ID         uuid.UUID  `json:"id" db:"id"`
+	Title      string     `json:"title" db:"title"`
+	StartAt    time.Time  `json:"start_at" db:"start_at"`
+	CaseNumber *string    `json:"case_number" db:"case_number"`
+	Location   *string    `json:"location" db:"location"`
+}
+
+type RecentActivity struct {
+	EventType  *string    `json:"event_type" db:"event_type"`
+	Title      string     `json:"title" db:"title"`
+	CaseNumber string     `json:"case_number" db:"case_number"`
+	EventDate  *time.Time `json:"event_date" db:"event_date"`
+}
+
+func (s *DashboardService) Get(ctx context.Context, tenantID uuid.UUID) (*DashboardData, error) {
+	now := time.Now()
+	today := now.Format("2006-01-02")
+	endOfWeek := now.AddDate(0, 0, 7-int(now.Weekday())).Format("2006-01-02")
+	endOfNextWeek := now.AddDate(0, 0, 14-int(now.Weekday())).Format("2006-01-02")
+	in7Days := now.AddDate(0, 0, 7).Format("2006-01-02")
+	startOfMonth := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, now.Location()).Format("2006-01-02")
+
+	data := &DashboardData{}
+
+	// Single query with CTEs for deadline + case summaries
+	summaryQuery := `
+		WITH deadline_stats AS (
+			SELECT
+				COUNT(*) FILTER (WHERE due_date < $2 AND status = 'pending') AS overdue_count,
+				COUNT(*) FILTER (WHERE due_date >= $2 AND due_date <= $3 AND status = 'pending') AS due_this_week,
+				COUNT(*) FILTER (WHERE due_date > $3 AND due_date <= $4 AND status = 'pending') AS due_next_week,
+				COUNT(*) FILTER (WHERE due_date > $4 AND status = 'pending') AS ok_count
+			FROM deadlines
+			WHERE tenant_id = $1
+		),
+		case_stats AS (
+			SELECT
+				COUNT(*) FILTER (WHERE status = 'active') AS active_count,
+				COUNT(*) FILTER (WHERE created_at >= $5::date AND status != 'archived') AS new_this_month,
+				COUNT(*) FILTER (WHERE status IN ('closed', 'archived')) AS closed_count
+			FROM cases
+			WHERE tenant_id = $1
+		)
+		SELECT
+			ds.overdue_count, ds.due_this_week, ds.due_next_week, ds.ok_count,
+			cs.active_count, cs.new_this_month, cs.closed_count
+		FROM deadline_stats ds, case_stats cs`
+
+	var summaryRow struct {
+		DeadlineSummary
+		CaseSummary
+	}
+	err := s.db.GetContext(ctx, &summaryRow, summaryQuery, tenantID, today, endOfWeek, endOfNextWeek, startOfMonth)
+	if err != nil {
+		return nil, fmt.Errorf("dashboard summary: %w", err)
+	}
+	data.DeadlineSummary = summaryRow.DeadlineSummary
+	data.CaseSummary = summaryRow.CaseSummary
+
+	// Upcoming deadlines (next 7 days)
+	deadlineQuery := `
+		SELECT d.id, d.title, d.due_date, c.case_number, c.title AS case_title, d.status
+		FROM deadlines d
+		JOIN cases c ON c.id = d.case_id AND c.tenant_id = d.tenant_id
+		WHERE d.tenant_id = $1 AND d.status = 'pending' AND d.due_date >= $2 AND d.due_date <= $3
+		ORDER BY d.due_date ASC`
+
+	data.UpcomingDeadlines = []UpcomingDeadline{}
+	if err := s.db.SelectContext(ctx, &data.UpcomingDeadlines, deadlineQuery, tenantID, today, in7Days); err != nil {
+		return nil, fmt.Errorf("dashboard upcoming deadlines: %w", err)
+	}
+
+	// Upcoming appointments (next 7 days)
+	appointmentQuery := `
+		SELECT a.id, a.title, a.start_at, c.case_number, a.location
+		FROM appointments a
+		LEFT JOIN cases c ON c.id = a.case_id AND c.tenant_id = a.tenant_id
+		WHERE a.tenant_id = $1 AND a.start_at >= $2::timestamp AND a.start_at < ($2::date + interval '7 days')
+		ORDER BY a.start_at ASC`
+
+	data.UpcomingAppointments = []UpcomingAppointment{}
+	if err := s.db.SelectContext(ctx, &data.UpcomingAppointments, appointmentQuery, tenantID, now); err != nil {
+		return nil, fmt.Errorf("dashboard upcoming appointments: %w", err)
+	}
+
+	// Recent activity (last 10 case events)
+	activityQuery := `
+		SELECT ce.event_type, ce.title, c.case_number, ce.event_date
+		FROM case_events ce
+		JOIN cases c ON c.id = ce.case_id AND c.tenant_id = ce.tenant_id
+		WHERE ce.tenant_id = $1
+		ORDER BY COALESCE(ce.event_date, ce.created_at) DESC
+		LIMIT 10`
+
+	data.RecentActivity = []RecentActivity{}
+	if err := s.db.SelectContext(ctx, &data.RecentActivity, activityQuery, tenantID); err != nil {
+		return nil, fmt.Errorf("dashboard recent activity: %w", err)
+	}
+
+	return data, nil
+}

backend/internal/services/dashboard_service_test.go

@@ -0,0 +1,33 @@
+package services
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDashboardDateCalculations(t *testing.T) {
+	// Verify the date range logic used in Get()
+	now := time.Date(2026, 3, 25, 14, 0, 0, 0, time.UTC) // Wednesday
+
+	today := now.Format("2006-01-02")
+	endOfWeek := now.AddDate(0, 0, 7-int(now.Weekday())).Format("2006-01-02")
+	endOfNextWeek := now.AddDate(0, 0, 14-int(now.Weekday())).Format("2006-01-02")
+	in7Days := now.AddDate(0, 0, 7).Format("2006-01-02")
+	startOfMonth := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, now.Location()).Format("2006-01-02")
+
+	if today != "2026-03-25" {
+		t.Errorf("today = %s, want 2026-03-25", today)
+	}
+	if endOfWeek != "2026-03-29" { // Sunday
+		t.Errorf("endOfWeek = %s, want 2026-03-29", endOfWeek)
+	}
+	if endOfNextWeek != "2026-04-05" {
+		t.Errorf("endOfNextWeek = %s, want 2026-04-05", endOfNextWeek)
+	}
+	if in7Days != "2026-04-01" {
+		t.Errorf("in7Days = %s, want 2026-04-01", in7Days)
+	}
+	if startOfMonth != "2026-03-01" {
+		t.Errorf("startOfMonth = %s, want 2026-03-01", startOfMonth)
+	}
+}