feat: add linkedin and facebook feature flags, clean up dead code

- Register 'linkedin' FeatureGroup with routers.linkedin and
  api.linkedin_image_generation routers
- Register 'facebook' FeatureGroup with
  api.facebook_writer.routers:facebook_router
- Add 'linkedin' and 'facebook' profiles to PROFILE_GROUP_MAP
- Remove dead imports of linkedin_router, linkedin_image_router,
  and facebook_router from app.py (router manager handles via
  CORE_ROUTER_REGISTRY)
- Add LINKEDIN and FACEBOOK keys to frontend FEATURE_KEYS
- Add route priorities for /linkedin-writer and /facebook-writer
- Change route gates from feature='social' to feature='linkedin'
  and feature='facebook' respectively

backend/alwrity_utils/feature_registry.py

@@ -62,6 +62,17 @@ FEATURE_GROUPS: Dict[str, FeatureGroup] = {
         features=("backlinking",),
         routers=("routers.backlink_outreach:router",),
     ),
+    "linkedin": FeatureGroup(
+        features=("linkedin",),
+        routers=(
+            "routers.linkedin:router",
+            "api.linkedin_image_generation:router",
+        ),
+    ),
+    "facebook": FeatureGroup(
+        features=("facebook",),
+        routers=("api.facebook_writer.routers:facebook_router",),
+    ),
 }
 
 
@@ -72,5 +83,7 @@ PROFILE_GROUP_MAP: Dict[str, Tuple[str, ...]] = {
     "youtube": ("core", "youtube"),
     "blog_writer": ("core", "blog_writer"),
     "backlinking": ("core", "backlinking"),
+    "linkedin": ("core", "linkedin"),
+    "facebook": ("core", "facebook"),
     "planning": ("core", "content_planning"),
 }