feat: add backend infrastructure - Express server, auth, CRUD APIs, DB migrations

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

src/db/connection.js

@@ -0,0 +1,64 @@
+const { Pool } = require('pg');
+
+let pool;
+
+async function connectDB() {
+  pool = new Pool({
+    connectionString: process.env.DATABASE_URL,
+    ssl: process.env.NODE_ENV === 'production' && process.env.DATABASE_URL && !process.env.DATABASE_URL.includes('localhost') && !process.env.DATABASE_URL.includes('postgres:') 
+      ? { rejectUnauthorized: false } 
+      : false
+  });
+  
+  // Test connection
+  const client = await pool.connect();
+  console.log('✅ PostgreSQL connected');
+  
+  // Run migrations
+  await runMigrations(client);
+  client.release();
+  
+  return pool;
+}
+
+async function runMigrations(client) {
+  // Create migrations tracking table
+  await client.query(`
+    CREATE TABLE IF NOT EXISTS schema_migrations (
+      id SERIAL PRIMARY KEY,
+      filename VARCHAR(255) UNIQUE NOT NULL,
+      applied_at TIMESTAMP DEFAULT NOW()
+    )
+  `);
+  
+  const fs = require('fs');
+  const path = require('path');
+  const migrationsDir = path.join(__dirname, 'migrations');
+  
+  if (!fs.existsSync(migrationsDir)) return;
+  
+  const files = fs.readdirSync(migrationsDir).sort();
+  for (const file of files) {
+    if (!file.endsWith('.sql')) continue;
+    
+    const { rows } = await client.query(
+      'SELECT id FROM schema_migrations WHERE filename = $1',
+      [file]
+    );
+    if (rows.length > 0) continue;
+    
+    const sql = fs.readFileSync(path.join(migrationsDir, file), 'utf8');
+    await client.query(sql);
+    await client.query(
+      'INSERT INTO schema_migrations (filename) VALUES ($1)',
+      [file]
+    );
+    console.log(`✅ Migration applied: ${file}`);
+  }
+}
+
+function getPool() {
+  return pool;
+}
+
+module.exports = { connectDB, getPool };