feat(health): add external URL column, backfill domains, thread through repo

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/health/registry.test.js

@@ -30,4 +30,12 @@ describe('registry', () => {
     expect(after.every(s => s.source === 'manual' && s.enabled)).toBe(true);
     expect(await seedFromConfig()).toBe(0);   // table not empty → no-op
   });
+
+  it('persists and returns external on create/get/update', async () => {
+    const id = 'ext-test';
+    await services.create({ id, name: 'Ext', url: 'http://10.0.0.1', external: 'https://ext.example.com' });
+    expect((await services.get(id)).external).toBe('https://ext.example.com');
+    const upd = await services.update(id, { external: 'https://ext2.example.com' });
+    expect(upd.external).toBe('https://ext2.example.com');
+  });
 });