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>

vite.config.ts

@@ -16,11 +16,11 @@ export default defineConfig({
     allowedHosts: ['hexifyer.davoryn.de'],
     proxy: {
       '/api': {
-        target: 'http://localhost:3001',
+        target: 'http://localhost:3002',
         changeOrigin: true,
       },
       '/tiles': {
-        target: 'http://localhost:3001',
+        target: 'http://localhost:3002',
         changeOrigin: true,
       },
     },