feat: Brainstorm Topics with GSC + Issue #518 fixes + Blog Editor enhancements

Issue #518 - Subscription not updating after checkout:
- Fix stale closure in SubscriptionContext checkout polling (use subscriptionRef)
- Move checkout success polling from InitialRouteHandler into SubscriptionContext
- Remove redundant polling code from InitialRouteHandler
- Fix plan label: 'Free' instead of 'No Plan', proper capitalization
- Add plan refresh button in UserBadge
- Add 'View Costing Details' to UserBadge dropdown
- Rename 'ALwrity Podcast Maker' to 'Podcast Creator' across UI
- Clean subscription=success URL param after verification

Blog Writer WYSIWYG Editor enhancements:
- Per-section preview toggle (view/edit icons)
- Enhanced hover-based toolbar
- Circular SVG progress stats bar with detailed tooltip
- Research tool chips in stats bar footer
- Per-section TTS with useTextToSpeech hook (browser native)
- Full blog preview modal with print/PDF support
- PlayAllTTSButton: sequential playback with progress bar
- OnThisPageNav: floating sidebar with scroll tracking
- Section data attributes for scroll anchoring

GSC Brainstorm Topics feature:
- Backend: gsc_brainstorm_service.py (rule-based + LLM recommendations)
- Backend: POST /gsc/brainstorm endpoint with 3-word minimum validation
- Frontend: gscBrainstorm.ts API client
- Frontend: useGSCBrainstormConnection hook (popup OAuth, no /onboarding redirect)
- Frontend: useGSCBrainstorm hook (connect check + brainstorm call)
- Frontend: GSCBrainstormModal (3-tab results: Opportunities, Gaps, AI Recs)
- Frontend: BrainstormButton (visible at 3+ words, GSC connect overlay)
- Wire BrainstormButton into ManualResearchForm and ResearchAction
- Add blog_writer to gsc_auth router features for ALWRITY_ENABLED_FEATURES

backend/main.py

@@ -81,6 +81,8 @@ from routers.campaign_creator import router as campaign_creator_router
 # Import hallucination detector router
 from api.hallucination_detector import router as hallucination_detector_router
 from api.writing_assistant import router as writing_assistant_router
+from api.charts import router as charts_router
+from api.links import router as links_router
 
 # Import research configuration router
 from api.research_config import router as research_config_router
@@ -254,6 +256,10 @@ router_manager.include_core_routers()
 router_manager.include_router_safely(subscription_router, "subscription")
 # Include hallucination detector explicitly (router_manager may skip silently on import failure)
 router_manager.include_router_safely(hallucination_detector_router, "hallucination_detector")
+# Include charts router (shared chart generation for blog writer, podcast, etc.)
+router_manager.include_router_safely(charts_router, "charts")
+# Include links router (internal & external link search and rewording)
+router_manager.include_router_safely(links_router, "links")
 router_manager.include_optional_routers()
 
 # SEO Dashboard endpoints