Phase 3: Express backend, SQLite persistence, auto-save

- server/db.ts: sql.js with migration system (hex_maps, hexes, hex_features)
- server/routes/maps.ts: CRUD for hex maps
- server/routes/hexes.ts: Bulk hex upsert, region load, sparse storage
- server/index.ts: Express 5, CORS, tile serving, SPA fallback
- src/data/api-client.ts: Frontend HTTP client for all API endpoints
- src/main.ts: Auto-save with 1s debounce, load map state on startup
- Port 3002 (Kiepenkerl uses 3001)
- Graceful fallback when API unavailable (works without server too)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -5,7 +5,7 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev": "concurrently \"vite\" \"tsx watch server/index.ts\"",
+    "dev": "concurrently \"vite --host 127.0.0.1 --port 5174\" \"tsx watch server/index.ts\"",
     "build": "vite build",
     "preview": "vite preview",
     "test": "vitest run",