test: e2e + unit tests for supervisor, proxy, and feature flags

- test_supervisor.py: 28 tests covering load_workflows, resolve_schedule,
  is_due, topological_waves, and proxy round-robin / sticky selection
- test_feature_flags.py: 31 tests covering migration 0019, is_flag_enabled,
  feature_gate decorator, admin toggle routes, and full toggle e2e flows
- conftest.py: seed feature flags with production defaults (markets=1,
  others=0) so all routes behave consistently in tests
- Fix is_flag_enabled bug: replace non-existent db.execute_fetchone()
  with fetch_one() helper
- Update 4 test_waitlist / test_businessplan tests that relied on
  WAITLIST_MODE patches — now enable the relevant DB flag instead

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/tests/test_businessplan.py

@@ -255,6 +255,10 @@ class TestExportRoutes:
         assert resp.status_code == 302
 
     async def test_export_page_shows_scenarios(self, auth_client, db, scenario):
+        await db.execute(
+            "INSERT OR REPLACE INTO feature_flags (name, enabled, description) VALUES ('planner_export', 1, '')"
+        )
+        await db.commit()
         resp = await auth_client.get("/en/planner/export")
         assert resp.status_code == 200
         html = (await resp.data).decode()