Add PostgreSQL schema and migration runner

All tables per PRD data model with default config seeds.
Migration runner tracks applied migrations in DB.

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

db/migrations/001_initial_schema.js

@@ -0,0 +1,51 @@
+const fs = require('fs');
+const path = require('path');
+
+async function runMigrations(pool) {
+  // Create migrations tracking table if it doesn't exist
+  await pool.query(`
+    CREATE TABLE IF NOT EXISTS migrations (
+      id         SERIAL PRIMARY KEY,
+      name       TEXT NOT NULL UNIQUE,
+      applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+    )
+  `);
+
+  // Read all .sql files in this directory, sorted by name
+  const migrationsDir = __dirname;
+  const sqlFiles = fs
+    .readdirSync(migrationsDir)
+    .filter((f) => f.endsWith('.sql'))
+    .sort();
+
+  for (const file of sqlFiles) {
+    // Check if this migration has already been applied
+    const { rows } = await pool.query(
+      'SELECT id FROM migrations WHERE name = $1',
+      [file]
+    );
+
+    if (rows.length > 0) {
+      continue; // already applied
+    }
+
+    const sql = fs.readFileSync(path.join(migrationsDir, file), 'utf8');
+
+    // Run the migration in a transaction
+    const client = await pool.connect();
+    try {
+      await client.query('BEGIN');
+      await client.query(sql);
+      await client.query('INSERT INTO migrations (name) VALUES ($1)', [file]);
+      await client.query('COMMIT');
+      console.log(`Migration applied: ${file}`);
+    } catch (err) {
+      await client.query('ROLLBACK');
+      throw new Error(`Migration failed for ${file}: ${err.message}`);
+    } finally {
+      client.release();
+    }
+  }
+}
+
+module.exports = { runMigrations };