feat: integrate schema initialization into server startup (Phase 3)

- Add schema initialization call after database connection
- Initialize schema before handler creation
- Fatal on failure (schema is critical for app to function)
- Clear log messages show initialization progress

Server startup flow:
1. Load config
2. Connect to database
3. Initialize schema (NEW - ensures all tables/functions exist)
4. Create handlers and services
5. Start server

cmd/server/main.go

@@ -78,6 +78,14 @@ func main() {
 
 	queries := database.New(dbPool)
 
+	// Initialize database schema
+	log.Println("🔧 Ensuring database schema is initialized...")
+	ctx := context.Background()
+	if err := database.Initialize(ctx, dbPool); err != nil {
+		log.Fatal("❌ Database schema initialization failed:", err)
+	}
+	log.Println("✅ Database schema initialized and verified, starting server...")
+
 	// Create login attempt tracker: 5 failed attempts = 15 minute lockout
 	loginAttemptTracker := ratelimit.NewLoginAttemptTracker(5, 15*time.Minute, 5*time.Minute)