06/16 Phase 6 foundation: admin blueprint, audit log, user management

Adds the admin backend foundation: AuditLog + Setting models/migration,
an admin-only dashboard with KPI cards, and user management (search,
ban/suspend/activate, tier override, trust adjust) with audit logging
on every write action. Smoke suite extended to 64 checks.

app/__init__.py

@@ -55,6 +55,7 @@ def _register_blueprints(app):
     from app.blueprints.messaging.routes import messaging_bp
     from app.blueprints.payments.routes import payments_bp
     from app.blueprints.ads.routes import ads_bp
+    from app.blueprints.admin.routes import admin_bp
     app.register_blueprint(main_bp)
     app.register_blueprint(auth_bp)
     app.register_blueprint(i18n_bp)
@@ -62,6 +63,7 @@ def _register_blueprints(app):
     app.register_blueprint(messaging_bp)
     app.register_blueprint(payments_bp)
     app.register_blueprint(ads_bp)
+    app.register_blueprint(admin_bp)
 
 
 def _register_errorhandlers(app):