feat: add appointment CRUD backend (Phase 1D)

- AppointmentService with tenant-scoped List, GetByID, Create, Update, Delete
- List supports filtering by case_id, appointment_type, and date range (start_from/start_to)
- AppointmentHandler with JSON request/response handling and input validation
- Router wired up: GET/POST /api/appointments, PUT/DELETE /api/appointments/{id}

backend/internal/handlers/appointments.go

@@ -0,0 +1,216 @@
+package handlers
+
+import (
+	"database/sql"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"time"
+
+	"github.com/google/uuid"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+type AppointmentHandler struct {
+	svc *services.AppointmentService
+}
+
+func NewAppointmentHandler(svc *services.AppointmentService) *AppointmentHandler {
+	return &AppointmentHandler{svc: svc}
+}
+
+func (h *AppointmentHandler) List(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusUnauthorized, "missing tenant")
+		return
+	}
+
+	filter := services.AppointmentFilter{}
+
+	if v := r.URL.Query().Get("case_id"); v != "" {
+		id, err := uuid.Parse(v)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "invalid case_id")
+			return
+		}
+		filter.CaseID = &id
+	}
+	if v := r.URL.Query().Get("type"); v != "" {
+		filter.Type = &v
+	}
+	if v := r.URL.Query().Get("start_from"); v != "" {
+		t, err := time.Parse(time.RFC3339, v)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "invalid start_from (use RFC3339)")
+			return
+		}
+		filter.StartFrom = &t
+	}
+	if v := r.URL.Query().Get("start_to"); v != "" {
+		t, err := time.Parse(time.RFC3339, v)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "invalid start_to (use RFC3339)")
+			return
+		}
+		filter.StartTo = &t
+	}
+
+	appointments, err := h.svc.List(r.Context(), tenantID, filter)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list appointments")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, appointments)
+}
+
+type createAppointmentRequest struct {
+	CaseID          *uuid.UUID `json:"case_id"`
+	Title           string     `json:"title"`
+	Description     *string    `json:"description"`
+	StartAt         time.Time  `json:"start_at"`
+	EndAt           *time.Time `json:"end_at"`
+	Location        *string    `json:"location"`
+	AppointmentType *string    `json:"appointment_type"`
+}
+
+func (h *AppointmentHandler) Create(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusUnauthorized, "missing tenant")
+		return
+	}
+
+	var req createAppointmentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+	if req.Title == "" {
+		writeError(w, http.StatusBadRequest, "title is required")
+		return
+	}
+	if req.StartAt.IsZero() {
+		writeError(w, http.StatusBadRequest, "start_at is required")
+		return
+	}
+
+	appt := &models.Appointment{
+		TenantID:        tenantID,
+		CaseID:          req.CaseID,
+		Title:           req.Title,
+		Description:     req.Description,
+		StartAt:         req.StartAt,
+		EndAt:           req.EndAt,
+		Location:        req.Location,
+		AppointmentType: req.AppointmentType,
+	}
+
+	if err := h.svc.Create(r.Context(), appt); err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to create appointment")
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, appt)
+}
+
+type updateAppointmentRequest struct {
+	CaseID          *uuid.UUID `json:"case_id"`
+	Title           string     `json:"title"`
+	Description     *string    `json:"description"`
+	StartAt         time.Time  `json:"start_at"`
+	EndAt           *time.Time `json:"end_at"`
+	Location        *string    `json:"location"`
+	AppointmentType *string    `json:"appointment_type"`
+}
+
+func (h *AppointmentHandler) Update(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusUnauthorized, "missing tenant")
+		return
+	}
+
+	id, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid appointment id")
+		return
+	}
+
+	// Fetch existing to verify ownership
+	existing, err := h.svc.GetByID(r.Context(), tenantID, id)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			writeError(w, http.StatusNotFound, "appointment not found")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, "failed to fetch appointment")
+		return
+	}
+
+	var req updateAppointmentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+	if req.Title == "" {
+		writeError(w, http.StatusBadRequest, "title is required")
+		return
+	}
+	if req.StartAt.IsZero() {
+		writeError(w, http.StatusBadRequest, "start_at is required")
+		return
+	}
+
+	existing.CaseID = req.CaseID
+	existing.Title = req.Title
+	existing.Description = req.Description
+	existing.StartAt = req.StartAt
+	existing.EndAt = req.EndAt
+	existing.Location = req.Location
+	existing.AppointmentType = req.AppointmentType
+
+	if err := h.svc.Update(r.Context(), existing); err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to update appointment")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, existing)
+}
+
+func (h *AppointmentHandler) Delete(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusUnauthorized, "missing tenant")
+		return
+	}
+
+	id, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid appointment id")
+		return
+	}
+
+	if err := h.svc.Delete(r.Context(), tenantID, id); err != nil {
+		writeError(w, http.StatusNotFound, "appointment not found")
+		return
+	}
+
+	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})
+}