feat: Phase A backend — notes CRUD, detail endpoints, dashboard fix

- Create kanzlai.notes table (polymorphic FK with CHECK constraint,
  partial indexes, RLS)
- Add Note model, NoteService (ListByParent, Create, Update, Delete),
  and NoteHandler with endpoints: GET/POST /api/notes, PUT/DELETE /api/notes/{id}
- Add GET /api/deadlines/{deadlineID} detail endpoint
- Add GET /api/appointments/{id} detail endpoint
- Add GET /api/case-events/{id} detail endpoint (new CaseEventHandler)
- Fix dashboard query: add case_id to upcoming_deadlines SELECT,
  add id and case_id to recent_activity SELECT
- Register all new routes in router.go

backend/internal/services/dashboard_service.go

@@ -42,6 +42,7 @@ type UpcomingDeadline struct {
 	ID         uuid.UUID `json:"id" db:"id"`
 	Title      string    `json:"title" db:"title"`
 	DueDate    string    `json:"due_date" db:"due_date"`
+	CaseID     uuid.UUID `json:"case_id" db:"case_id"`
 	CaseNumber string    `json:"case_number" db:"case_number"`
 	CaseTitle  string    `json:"case_title" db:"case_title"`
 	Status     string    `json:"status" db:"status"`
@@ -56,8 +57,10 @@ type UpcomingAppointment struct {
 }
 
 type RecentActivity struct {
+	ID         uuid.UUID  `json:"id" db:"id"`
 	EventType  *string    `json:"event_type" db:"event_type"`
 	Title      string     `json:"title" db:"title"`
+	CaseID     uuid.UUID  `json:"case_id" db:"case_id"`
 	CaseNumber string     `json:"case_number" db:"case_number"`
 	EventDate  *time.Time `json:"event_date" db:"event_date"`
 }
@@ -109,7 +112,7 @@ func (s *DashboardService) Get(ctx context.Context, tenantID uuid.UUID) (*Dashbo
 
 	// Upcoming deadlines (next 7 days)
 	deadlineQuery := `
-		SELECT d.id, d.title, d.due_date, c.case_number, c.title AS case_title, d.status
+		SELECT d.id, d.title, d.due_date, d.case_id, 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
@@ -135,7 +138,7 @@ func (s *DashboardService) Get(ctx context.Context, tenantID uuid.UUID) (*Dashbo
 
 	// Recent activity (last 10 case events)
 	activityQuery := `
-		SELECT ce.event_type, ce.title, c.case_number, ce.event_date
+		SELECT ce.id, ce.event_type, ce.title, ce.case_id, 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

backend/internal/services/note_service.go

@@ -0,0 +1,120 @@
+package services
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+type NoteService struct {
+	db *sqlx.DB
+}
+
+func NewNoteService(db *sqlx.DB) *NoteService {
+	return &NoteService{db: db}
+}
+
+// ListByParent returns all notes for a given parent entity, scoped to tenant.
+func (s *NoteService) ListByParent(ctx context.Context, tenantID uuid.UUID, parentType string, parentID uuid.UUID) ([]models.Note, error) {
+	col, err := parentColumn(parentType)
+	if err != nil {
+		return nil, err
+	}
+
+	query := fmt.Sprintf(
+		`SELECT id, tenant_id, case_id, deadline_id, appointment_id, case_event_id,
+		        content, created_by, created_at, updated_at
+		 FROM notes
+		 WHERE tenant_id = $1 AND %s = $2
+		 ORDER BY created_at DESC`, col)
+
+	var notes []models.Note
+	if err := s.db.SelectContext(ctx, &notes, query, tenantID, parentID); err != nil {
+		return nil, fmt.Errorf("listing notes by %s: %w", parentType, err)
+	}
+	if notes == nil {
+		notes = []models.Note{}
+	}
+	return notes, nil
+}
+
+type CreateNoteInput struct {
+	CaseID        *uuid.UUID `json:"case_id,omitempty"`
+	DeadlineID    *uuid.UUID `json:"deadline_id,omitempty"`
+	AppointmentID *uuid.UUID `json:"appointment_id,omitempty"`
+	CaseEventID   *uuid.UUID `json:"case_event_id,omitempty"`
+	Content       string     `json:"content"`
+}
+
+// Create inserts a new note.
+func (s *NoteService) Create(ctx context.Context, tenantID uuid.UUID, createdBy *uuid.UUID, input CreateNoteInput) (*models.Note, error) {
+	id := uuid.New()
+	now := time.Now().UTC()
+
+	query := `INSERT INTO notes (id, tenant_id, case_id, deadline_id, appointment_id, case_event_id, content, created_by, created_at, updated_at)
+	          VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $9)
+	          RETURNING id, tenant_id, case_id, deadline_id, appointment_id, case_event_id, content, created_by, created_at, updated_at`
+
+	var n models.Note
+	err := s.db.GetContext(ctx, &n, query,
+		id, tenantID, input.CaseID, input.DeadlineID, input.AppointmentID, input.CaseEventID,
+		input.Content, createdBy, now)
+	if err != nil {
+		return nil, fmt.Errorf("creating note: %w", err)
+	}
+	return &n, nil
+}
+
+// Update modifies a note's content.
+func (s *NoteService) Update(ctx context.Context, tenantID, noteID uuid.UUID, content string) (*models.Note, error) {
+	query := `UPDATE notes SET content = $1, updated_at = $2
+	          WHERE id = $3 AND tenant_id = $4
+	          RETURNING id, tenant_id, case_id, deadline_id, appointment_id, case_event_id, content, created_by, created_at, updated_at`
+
+	var n models.Note
+	err := s.db.GetContext(ctx, &n, query, content, time.Now().UTC(), noteID, tenantID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("updating note: %w", err)
+	}
+	return &n, nil
+}
+
+// Delete removes a note.
+func (s *NoteService) Delete(ctx context.Context, tenantID, noteID uuid.UUID) error {
+	result, err := s.db.ExecContext(ctx, "DELETE FROM notes WHERE id = $1 AND tenant_id = $2", noteID, tenantID)
+	if err != nil {
+		return fmt.Errorf("deleting note: %w", err)
+	}
+	rows, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("checking delete result: %w", err)
+	}
+	if rows == 0 {
+		return fmt.Errorf("note not found")
+	}
+	return nil
+}
+
+func parentColumn(parentType string) (string, error) {
+	switch parentType {
+	case "case":
+		return "case_id", nil
+	case "deadline":
+		return "deadline_id", nil
+	case "appointment":
+		return "appointment_id", nil
+	case "case_event":
+		return "case_event_id", nil
+	default:
+		return "", fmt.Errorf("invalid parent type: %s", parentType)
+	}
+}