feat: add backlinking feature flag following blog_writer pattern

- Register 'backlinking' FeatureGroup in feature_registry.py with
  routers=routers.backlink_outreach:router
- Add 'backlinking' profile to PROFILE_GROUP_MAP (core + backlinking)
- Add backlink_outreach to OPTIONAL_ROUTER_REGISTRY with
  features={'all', 'backlinking'}
- Remove direct import/include of backlink_outreach from app.py
  (router manager handles both 'all' and 'backlinking' modes)
- Add BACKLINKING key to FEATURE_KEYS and route priority in
  frontend demoMode.ts
- Change frontend route gate from feature='seo' to feature='backlinking'
  so ALWRITY_ENABLED_FEATURES=backlinking enables the route

backend/alwrity_utils/feature_registry.py

@@ -58,6 +58,10 @@ FEATURE_GROUPS: Dict[str, FeatureGroup] = {
             "api.blog_writer.seo_analysis:router",
         ),
     ),
+    "backlinking": FeatureGroup(
+        features=("backlinking",),
+        routers=("routers.backlink_outreach:router",),
+    ),
 }
 
 
@@ -67,5 +71,6 @@ PROFILE_GROUP_MAP: Dict[str, Tuple[str, ...]] = {
     "podcast": ("core", "podcast"),
     "youtube": ("core", "youtube"),
     "blog_writer": ("core", "blog_writer"),
+    "backlinking": ("core", "backlinking"),
     "planning": ("core", "content_planning"),
 }

backend/alwrity_utils/router_manager.py

@@ -67,6 +67,7 @@ OPTIONAL_ROUTER_REGISTRY = [
     {"name": "oauth_token_monitoring", "module": "api.oauth_token_monitoring_routes", "attr": "router", "features": {"all", "core"}},
     {"name": "agents", "module": "api.agents_api", "attr": "router", "features": {"all"}},
     {"name": "today_workflow", "module": "api.today_workflow", "attr": "router", "features": {"all"}},
+    {"name": "backlink_outreach", "module": "routers.backlink_outreach", "attr": "router", "features": {"all", "backlinking"}},
 ]
 
 OPTIONAL_MODULE_MATRIX = {