Add Node.js/Express API service for booking backend

- New api/ service: Express + better-sqlite3, health check at GET /api/health,
  POST /api/bookings stores sessions with all required fields
- Dockerfile with Alpine build deps for native sqlite3 module
- docker-compose.yml: api service with volume mounts for data, signed-contracts, contracts
- nginx.conf: proxy /api/ to api:3001; Immich regex locations remain higher priority
- .gitignore: exclude SQLite db file and signed PDFs from version control

Closes #1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/db.js

@@ -0,0 +1,31 @@
+const Database = require('better-sqlite3');
+const path = require('path');
+const fs = require('fs');
+
+const dataDir = path.join(__dirname, 'data');
+if (!fs.existsSync(dataDir)) fs.mkdirSync(dataDir, { recursive: true });
+
+const db = new Database(path.join(dataDir, 'bookings.db'));
+
+db.exec(`
+  CREATE TABLE IF NOT EXISTS bookings (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    created_at TEXT DEFAULT (datetime('now')),
+    client_name TEXT,
+    client_email TEXT,
+    client_phone TEXT,
+    client_sub TEXT,
+    session_date TEXT,
+    session_type TEXT,
+    session_length TEXT,
+    location TEXT,
+    contract_signed_at TEXT,
+    contract_pdf_path TEXT,
+    payment_status TEXT DEFAULT 'pending',
+    payment_notified_at TEXT,
+    status TEXT DEFAULT 'pending',
+    notes TEXT
+  )
+`);
+
+module.exports = db;