chore: remainder — backend test infra, agent config, docker, i18n, frontend ui

- Backend: alembic env, config manager/models, dependencies, translate plugin
- Backend tests: async_sync_regression, integration tests, git services, test_agent
- Docker: docker-compose.yml updates
- Agent: qa-tester.md update, semantics-testing SKILL.md update
- Frontend: TopNavbar, sidebarNavigation, FeaturesSettings, FeatureGate
- i18n: assistant.json en/ru locale updates
- New: frontend/src/lib/components/agent/ directory

backend/src/api/routes/translate/_router.py

@@ -1,14 +1,23 @@
 # #region TranslateRouterModule [C:1] [TYPE Module] [SEMANTICS fastapi, translate, api]
-# @BRIEF APIRouter instance for translate routes.
+# @BRIEF APIRouter instance for translate routes with feature flag gating.
 # @LAYER API
+# @RELATION DEPENDS_ON -> [require_feature]
 
-from fastapi import APIRouter
+from fastapi import APIRouter, Depends
+
+from ....dependencies import require_feature
 
 # #region translate_router [TYPE Global]
 # @ingroup Api
 # @BRIEF APIRouter instance for all translate sub-routes.
+# @INVARIANT All translate routes are gated by the 'translate' feature flag.
+#            Sub-features (scheduling, dictionaries) have their own gating.
 
-router = APIRouter(prefix="/api/translate", tags=["translate"])
+router = APIRouter(
+    prefix="/api/translate",
+    tags=["translate"],
+    dependencies=[Depends(require_feature("translate"))],
+)
 # #endregion translate_router
 
 # #endregion TranslateRouterModule