perf(api): bound worker pools and add telemetry

Share one configured PostgreSQL pool across worker repositories and make API and worker connection budgets explicit.

Add privacy-safe aggregate request, query, pool, sync, and outbox telemetry, a loopback-only representative load fixture, bounded worker shutdown, and focused regression and integration coverage.

Document the database-wide budget formula and defer pg_stat_statements activation to a reviewed migration and planned restart.

apps/api/test/load.loopback.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest';
+import { requireLocalApi, requireLoopback } from '../src/load/loopback.js';
+
+describe('representative load fixture boundary', () => {
+  it('accepts only loopback API and PostgreSQL URLs', () => {
+    expect(requireLoopback('http://127.0.0.1:3003', 'API').hostname).toBe('127.0.0.1');
+    expect(requireLoopback('postgresql://sauci:test@localhost:5432/sauci', 'DATABASE').hostname).toBe('localhost');
+    expect(() => requireLoopback('https://api.sauci.example', 'API')).toThrow('must resolve to loopback');
+    expect(() => requireLoopback('postgresql://sauci:test@db.internal:5432/sauci', 'DATABASE')).toThrow('must resolve to loopback');
+  });
+
+  it('allows only the controlled local HTTP API port', () => {
+    expect(requireLocalApi('http://127.0.0.1:3003').port).toBe('3003');
+    expect(() => requireLocalApi('https://127.0.0.1:3003')).toThrow('must be http loopback');
+    expect(() => requireLocalApi('http://127.0.0.1:3004')).toThrow('must be http loopback');
+  });
+});