feat: AI-powered features — document drafting, case strategy, similar case finder (P2)

Backend:
- DraftDocument: Claude generates legal documents from case data + template type
  (14 template types: Klageschrift, UPC claims, Abmahnung, etc.)
- CaseStrategy: Opus-powered strategic analysis with next steps, risk assessment,
  and timeline optimization (structured tool output)
- FindSimilarCases: queries youpc.org Supabase for UPC cases, Claude ranks by
  relevance with explanations and key holdings

Endpoints: POST /api/ai/draft-document, /case-strategy, /similar-cases
All rate-limited (5 req/min) and permission-gated (PermAIExtraction).
YouPC database connection is optional (YOUPC_DATABASE_URL env var).

backend/cmd/server/main.go

@@ -5,6 +5,9 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/jmoiron/sqlx"
+	_ "github.com/lib/pq"
+
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/config"
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/db"
@@ -31,6 +34,21 @@ func main() {
 
 	authMW := auth.NewMiddleware(cfg.SupabaseJWTSecret, database)
 
+	// Optional: connect to youpc.org database for similar case finder
+	var youpcDB *sqlx.DB
+	if cfg.YouPCDatabaseURL != "" {
+		youpcDB, err = sqlx.Connect("postgres", cfg.YouPCDatabaseURL)
+		if err != nil {
+			slog.Warn("failed to connect to youpc.org database — similar case finder disabled", "error", err)
+			youpcDB = nil
+		} else {
+			youpcDB.SetMaxOpenConns(5)
+			youpcDB.SetMaxIdleConns(2)
+			defer youpcDB.Close()
+			slog.Info("connected to youpc.org database for similar case finder")
+		}
+	}
+
 	// Start CalDAV sync service
 	calDAVSvc := services.NewCalDAVService(database)
 	calDAVSvc.Start()
@@ -41,7 +59,7 @@ func main() {
 	notifSvc.Start()
 	defer notifSvc.Stop()
 
-	handler := router.New(database, authMW, cfg, calDAVSvc, notifSvc)
+	handler := router.New(database, authMW, cfg, calDAVSvc, notifSvc, youpcDB)
 
 	slog.Info("starting KanzlAI API server", "port", cfg.Port)
 	if err := http.ListenAndServe(":"+cfg.Port, handler); err != nil {