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>

server/db.ts

@@ -0,0 +1,113 @@
+import initSqlJs, { type Database } from 'sql.js';
+import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'fs';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const DB_PATH = process.env.DB_PATH || resolve(__dirname, '..', 'data', 'hexifyer.db');
+
+let db: Database;
+
+interface Migration {
+  name: string;
+  up: () => void;
+}
+
+const MIGRATIONS: Migration[] = [
+  {
+    name: '001-initial-schema',
+    up() {
+      db.run(`
+        CREATE TABLE IF NOT EXISTS hex_maps (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          name TEXT NOT NULL,
+          image_width INTEGER NOT NULL DEFAULT 8000,
+          image_height INTEGER NOT NULL DEFAULT 12000,
+          tile_url TEXT NOT NULL DEFAULT '/tiles/{z}/{x}/{y}.jpg',
+          min_zoom INTEGER NOT NULL DEFAULT 0,
+          max_zoom INTEGER NOT NULL DEFAULT 6,
+          hex_size REAL NOT NULL DEFAULT 48.0,
+          origin_x REAL NOT NULL DEFAULT 0.0,
+          origin_y REAL NOT NULL DEFAULT 0.0,
+          created_at TEXT DEFAULT (datetime('now')),
+          updated_at TEXT DEFAULT (datetime('now'))
+        )
+      `);
+
+      db.run(`
+        CREATE TABLE IF NOT EXISTS hexes (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          map_id INTEGER NOT NULL,
+          q INTEGER NOT NULL,
+          r INTEGER NOT NULL,
+          base_terrain TEXT NOT NULL DEFAULT 'plains',
+          updated_at TEXT DEFAULT (datetime('now')),
+          FOREIGN KEY (map_id) REFERENCES hex_maps(id) ON DELETE CASCADE,
+          UNIQUE(map_id, q, r)
+        )
+      `);
+
+      db.run(`
+        CREATE TABLE IF NOT EXISTS hex_features (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          hex_id INTEGER NOT NULL,
+          terrain_id TEXT NOT NULL,
+          edge_mask INTEGER NOT NULL,
+          FOREIGN KEY (hex_id) REFERENCES hexes(id) ON DELETE CASCADE
+        )
+      `);
+
+      db.run('CREATE INDEX IF NOT EXISTS idx_hexes_map_coord ON hexes(map_id, q, r)');
+      db.run('CREATE INDEX IF NOT EXISTS idx_hex_features_hex ON hex_features(hex_id)');
+    },
+  },
+];
+
+function runMigrations(): void {
+  db.run(`
+    CREATE TABLE IF NOT EXISTS schema_migrations (
+      name TEXT PRIMARY KEY,
+      applied_at TEXT DEFAULT (datetime('now'))
+    )
+  `);
+
+  const applied = new Set<string>();
+  const rows = db.exec('SELECT name FROM schema_migrations');
+  if (rows.length > 0) {
+    for (const row of rows[0].values) applied.add(row[0] as string);
+  }
+
+  for (const m of MIGRATIONS) {
+    if (applied.has(m.name)) continue;
+    console.log(`[db] Running migration: ${m.name}`);
+    m.up();
+    db.run('INSERT INTO schema_migrations (name) VALUES (?)', [m.name]);
+  }
+}
+
+export async function initDb(): Promise<Database> {
+  const SQL = await initSqlJs();
+
+  if (existsSync(DB_PATH)) {
+    const buf = readFileSync(DB_PATH);
+    db = new SQL.Database(buf);
+    console.log(`[db] Loaded existing database from ${DB_PATH}`);
+  } else {
+    db = new SQL.Database();
+    console.log('[db] Created new database');
+  }
+
+  runMigrations();
+  saveDb();
+  return db;
+}
+
+export function saveDb(): void {
+  mkdirSync(dirname(DB_PATH), { recursive: true });
+  const data = db.export();
+  writeFileSync(DB_PATH, Buffer.from(data));
+}
+
+export function getDb(): Database {
+  return db;
+}