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/services/llm_providers/wavespeed_provider.py

@@ -353,7 +353,11 @@ def wavespeed_text_response(
         
         raise Exception(f"WaveSpeed text generation failed: {str(e)}")
 
-@retry(wait=wait_random_exponential(min=1, max=60), stop=stop_after_attempt(6))
+@retry(
+    retry=retry_if_exception(_should_retry_wavespeed_error),
+    wait=wait_random_exponential(min=1, max=60),
+    stop=stop_after_attempt(6),
+)
 def wavespeed_structured_json_response(
     prompt: str,
     schema: Dict[str, Any],
@@ -608,4 +612,20 @@ def wavespeed_structured_json_response(
         error_msg = str(e) if str(e) else repr(e)
         error_type = type(e).__name__
         logger.error(f"❌ WaveSpeed structured JSON generation failed [{error_type}]: {error_msg}")
+        
+        # Surface balance/quota errors as HTTPException so upstream can show user-friendly messages
+        from fastapi import HTTPException
+        if "balance_not_enough" in error_msg or "403" in error_msg or "PermissionDenied" in error_type:
+            raise HTTPException(
+                status_code=403,
+                detail={
+                    "error": "insufficient_balance",
+                    "message": "WaveSpeed API balance is insufficient. Please top up your WaveSpeed account or switch to a different provider.",
+                    "usage_info": {
+                        "error_type": "insufficient_balance",
+                        "provider": "wavespeed",
+                        "suggestion": "Set GPT_PROVIDER=google in your environment to use Gemini instead, or add credits to your WaveSpeed account."
+                    }
+                }
+            )
         raise Exception(f"WaveSpeed structured JSON generation failed: {error_msg}")