feat: add deadline CRUD, calculator, and holiday services (Phase 1C)

- Holiday service with German federal holidays, Easter calculation, DB loading
- Deadline calculator adapted from youpc.org (duration calc + non-working day adjustment)
- Deadline CRUD service (tenant-scoped: list, create, update, complete, delete)
- Deadline rule service (list, filter by proceeding type, hierarchical rule trees)
- HTTP handlers for all endpoints with tenant resolution via X-Tenant-ID header
- Router wired with all new endpoints under /api/
- Tests for holiday and calculator services (8 passing)

backend/internal/router/router.go

@@ -4,12 +4,25 @@ import (
 	"encoding/json"
 	"net/http"
 
-	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
-
 	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/handlers"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
 )
 
 func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
+	// Services
+	holidaySvc := services.NewHolidayService(db)
+	deadlineSvc := services.NewDeadlineService(db)
+	deadlineRuleSvc := services.NewDeadlineRuleService(db)
+	calculator := services.NewDeadlineCalculator(holidaySvc)
+
+	// Handlers
+	deadlineH := handlers.NewDeadlineHandlers(deadlineSvc, db)
+	ruleH := handlers.NewDeadlineRuleHandlers(deadlineRuleSvc)
+	calcH := handlers.NewCalculateHandlers(calculator, deadlineRuleSvc)
+
 	mux := http.NewServeMux()
 
 	// Public routes
@@ -17,8 +30,23 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 
 	// Authenticated API routes
 	api := http.NewServeMux()
+
+	// Deadline CRUD (case-scoped)
+	api.HandleFunc("GET /api/cases/{caseID}/deadlines", deadlineH.ListForCase)
+	api.HandleFunc("POST /api/cases/{caseID}/deadlines", deadlineH.Create)
+	api.HandleFunc("PUT /api/deadlines/{deadlineID}", deadlineH.Update)
+	api.HandleFunc("PATCH /api/deadlines/{deadlineID}/complete", deadlineH.Complete)
+	api.HandleFunc("DELETE /api/deadlines/{deadlineID}", deadlineH.Delete)
+
+	// Deadline rules (public reference data, but behind auth)
+	api.HandleFunc("GET /api/deadline-rules", ruleH.List)
+	api.HandleFunc("GET /api/deadline-rules/{type}", ruleH.GetRuleTree)
+
+	// Deadline calculator
+	api.HandleFunc("POST /api/deadlines/calculate", calcH.Calculate)
+
+	// Placeholder routes (not yet implemented)
 	api.HandleFunc("GET /api/cases", placeholder("cases"))
-	api.HandleFunc("GET /api/deadlines", placeholder("deadlines"))
 	api.HandleFunc("GET /api/appointments", placeholder("appointments"))
 	api.HandleFunc("GET /api/documents", placeholder("documents"))