feat: production hardening — slog, rate limiting, integration tests, seed data (Phase 4)

- Structured logging: replace log.* with log/slog JSON output across backend
- Request logger middleware: logs method, path, status, duration for all non-health requests
- Rate limiting: token bucket (5 req/min, burst 10) on AI endpoints (/api/ai/*)
- Integration tests: full critical path test (auth -> create case -> add deadline -> dashboard)
- Seed demo data: 1 tenant, 5 cases with deadlines/appointments/parties/events
- docker-compose.yml: add all required env vars (DATABASE_URL, SUPABASE_*, ANTHROPIC_API_KEY)
- .env.example: document all env vars including DATABASE_URL and CalDAV note

backend/cmd/server/main.go

@@ -1,25 +1,31 @@
 package main
 
 import (
-	"log"
+	"log/slog"
 	"net/http"
+	"os"
 
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/config"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/db"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/logging"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/router"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
 )
 
 func main() {
+	logging.Setup()
+
 	cfg, err := config.Load()
 	if err != nil {
-		log.Fatalf("Failed to load config: %v", err)
+		slog.Error("failed to load config", "error", err)
+		os.Exit(1)
 	}
 
 	database, err := db.Connect(cfg.DatabaseURL)
 	if err != nil {
-		log.Fatalf("Failed to connect to database: %v", err)
+		slog.Error("failed to connect to database", "error", err)
+		os.Exit(1)
 	}
 	defer database.Close()
 
@@ -32,8 +38,9 @@ func main() {
 
 	handler := router.New(database, authMW, cfg, calDAVSvc)
 
-	log.Printf("Starting KanzlAI API server on :%s", cfg.Port)
+	slog.Info("starting KanzlAI API server", "port", cfg.Port)
 	if err := http.ListenAndServe(":"+cfg.Port, handler); err != nil {
-		log.Fatal(err)
+		slog.Error("server failed", "error", err)
+		os.Exit(1)
 	}
 }