feat(CF-368): Use pgbouncer connection pooling via POSTGRES_PORT env

Changed hardcoded port 5432 to read from POSTGRES_PORT environment
variable to support pgbouncer connection pooling (port 6432).

Connection pooling reduces overhead for frequent queries and better
handles concurrent connections.

.env now configured with POSTGRES_PORT=6432 (pgbouncer).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/db.ts

@@ -5,7 +5,7 @@ const { Pool } = pg;
 // Uses DNS hostname (infra.agiliton.internal) via WireGuard DNS
 const config = {
   host: process.env.POSTGRES_HOST || 'infra.agiliton.internal',
-  port: 5432,
+  port: parseInt(process.env.POSTGRES_PORT || '5432'),
   database: 'agiliton',
   user: 'agiliton',
   password: 'QtqiwCOAUpQNF6pjzOMAREzUny2bY8V1',