feat(postgres): infrastructure setup and schema creation (tasks 1-2)

- Install pg (node-postgres) dependency
- Create backend/db.js connection pool module (max 10, auto-reconnect)
- Install Docker and spin up steam-postgres container on port 5433
- Create backend/db-schema.sql with complete Postgres DDL (24 tables)
- Replace findings_json blob with ivanti_findings table (individual rows)
- Merge notes/overrides into findings table columns
- Add proper indexes: state, bu_ownership, severity, composite
- Create backend/setup-postgres.js for idempotent schema initialization
- Add DATABASE_URL to .env and .env.example
- Update migration plan docs with Docker setup commands
- Verify: schema executes cleanly, pool connects, 24 tables created

backend/db.js

@@ -0,0 +1,43 @@
+// PostgreSQL Connection Pool
+// All route files import this module instead of receiving a sqlite3 `db` parameter.
+// Configured via DATABASE_URL environment variable.
+
+const { Pool } = require('pg');
+
+if (!process.env.DATABASE_URL) {
+    console.error('[DB] FATAL: DATABASE_URL environment variable is not set.');
+    console.error('[DB] Expected format: postgresql://user:password@host:port/database');
+    process.exit(1);
+}
+
+const pool = new Pool({
+    connectionString: process.env.DATABASE_URL,
+    max: 10,                        // Maximum connections in pool
+    idleTimeoutMillis: 30000,       // Close idle connections after 30s
+    connectionTimeoutMillis: 5000,  // Fail if connection takes >5s
+});
+
+// Log unexpected pool errors (connection drops, etc.)
+pool.on('error', (err) => {
+    console.error('[DB Pool] Unexpected error on idle client:', err.message);
+});
+
+// Track active connections and warn when approaching exhaustion
+let _activeCount = 0;
+pool.on('acquire', () => {
+    _activeCount++;
+    if (_activeCount >= 8) {
+        console.warn(`[DB Pool] WARNING: ${_activeCount}/10 connections active — approaching exhaustion`);
+    }
+});
+pool.on('release', () => { _activeCount--; });
+
+// Health check — verify connection on startup
+pool.query('SELECT NOW()')
+    .then(() => console.log('[DB Pool] Connected to PostgreSQL'))
+    .catch((err) => {
+        console.error('[DB Pool] Failed to connect:', err.message);
+        console.error('[DB Pool] Check DATABASE_URL and ensure Postgres is running on port 5433');
+    });
+
+module.exports = pool;