feature: add new chains & fix: connection pool leak

[ssejzer]

• Connection pool leak: The finally block in db.ts:308 had an inverted condition (if (this.connections.includes(conn)) return;) that skipped connection cleanup, leaking every DB connection until the pool filled to
  1000/1000. On cache miss, endpoints like /listProviders would hang forever waiting for a free connection. Fixed by adding the missing !.
• Broken .client.end() call: The leak fix exposed a second latent bug — (conn.db as any).client.end() threw TypeError because the drizzle ORM wrapper doesn't expose the raw postgres client at .client. This never
  crashed before because the inverted condition prevented the line from ever executing. Fixed by storing the raw postgres() sql client as sqlClient on the DbConnection interface and calling conn.sqlClient.end()
  directly.