Add full fediverse social service

Social blueprint with timeline, compose, search, follow/unfollow,
like/boost interactions, and notifications. Inbox handler extended
for Create/Update/Delete/Accept/Like/Announce with notification
creation. HTMX-powered infinite scroll and interaction buttons.
Nav updated with Timeline, Public, Search, and Notifications links.

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

app.py

@@ -13,6 +13,7 @@ from bp import (
     register_actors_bp,
     register_identity_bp,
     register_auth_bp,
+    register_social_bp,
 )
 
 
@@ -53,6 +54,7 @@ def create_app() -> "Quart":
     app.register_blueprint(register_actors_bp())
     app.register_blueprint(register_identity_bp())
     app.register_blueprint(register_auth_bp())
+    app.register_blueprint(register_social_bp())
 
     # --- home page ---
     @app.get("/")