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/server.js

@@ -0,0 +1,35 @@
+require('dotenv').config();
+const express = require('express');
+const cors = require('cors');
+const db = require('./db');
+
+const app = express();
+const PORT = process.env.PORT || 3001;
+
+app.use(cors({ origin: process.env.CORS_ORIGIN || '*', credentials: true }));
+app.use(express.json({ limit: '10mb' }));
+
+app.get('/api/health', (req, res) => {
+  res.json({ ok: true });
+});
+
+app.post('/api/bookings', (req, res) => {
+  const {
+    client_name, client_email, client_phone, client_sub,
+    session_date, session_type, session_length, location,
+  } = req.body;
+
+  if (!client_email || !session_date || !session_type || !session_length) {
+    return res.status(400).json({ error: 'Missing required fields' });
+  }
+
+  const result = db.prepare(`
+    INSERT INTO bookings
+      (client_name, client_email, client_phone, client_sub, session_date, session_type, session_length, location)
+    VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+  `).run(client_name, client_email, client_phone, client_sub, session_date, session_type, session_length, location);
+
+  res.status(201).json({ id: result.lastInsertRowid });
+});
+
+app.listen(PORT, () => console.log(`API listening on port ${PORT}`));