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

frontend/src/hooks/useGSCBrainstorm.ts

@@ -0,0 +1,102 @@
+import { useState, useCallback } from 'react';
+import { useAuth } from '@clerk/clerk-react';
+import {
+  gscBrainstormAPI,
+  BrainstormResult,
+  ContentOpportunity,
+  KeywordGap,
+  AIRecommendations,
+  BrainstormSummary,
+} from '../api/gscBrainstorm';
+import { useGSCBrainstormConnection } from './useGSCBrainstormConnection';
+
+interface UseGSCBrainstormReturn {
+  gscConnected: boolean;
+  gscSites: { siteUrl: string; permissionLevel: string }[] | null;
+  isConnecting: boolean;
+  connectError: string | null;
+  isBrainstorming: boolean;
+  brainstormError: string | null;
+  brainstormResult: BrainstormResult | null;
+  contentOpportunities: ContentOpportunity[];
+  keywordGaps: KeywordGap[];
+  aiRecommendations: AIRecommendations | null;
+  summary: BrainstormSummary | null;
+  connectGSC: () => Promise<void>;
+  brainstorm: (keywords: string, siteUrl?: string) => Promise<BrainstormResult | null>;
+  reset: () => void;
+}
+
+export const useGSCBrainstorm = (): UseGSCBrainstormReturn => {
+  const { getToken } = useAuth();
+  const {
+    gscConnected,
+    gscSites,
+    isConnecting,
+    connectError,
+    checkConnection,
+    connectGSC,
+  } = useGSCBrainstormConnection();
+
+  const [isBrainstorming, setIsBrainstorming] = useState(false);
+  const [brainstormError, setBrainstormError] = useState<string | null>(null);
+  const [brainstormResult, setBrainstormResult] = useState<BrainstormResult | null>(null);
+
+  const brainstorm = useCallback(
+    async (keywords: string, siteUrl?: string): Promise<BrainstormResult | null> => {
+      setIsBrainstorming(true);
+      setBrainstormError(null);
+
+      try {
+        gscBrainstormAPI.setAuthTokenGetter(async () => {
+          try {
+            return await getToken();
+          } catch {
+            return null;
+          }
+        });
+
+        const result = await gscBrainstormAPI.brainstorm(keywords, siteUrl);
+        setBrainstormResult(result);
+        return result;
+      } catch (error) {
+        const message =
+          error instanceof Error ? error.message : 'Failed to brainstorm topics. Please try again.';
+        setBrainstormError(message);
+        return null;
+      } finally {
+        setIsBrainstorming(false);
+      }
+    },
+    [getToken],
+  );
+
+  const reset = useCallback(() => {
+    setBrainstormResult(null);
+    setBrainstormError(null);
+    setIsBrainstorming(false);
+  }, []);
+
+  return {
+    gscConnected,
+    gscSites,
+    isConnecting,
+    connectError,
+    isBrainstorming,
+    brainstormError,
+    brainstormResult,
+    contentOpportunities: brainstormResult?.content_opportunities ?? [],
+    keywordGaps: brainstormResult?.keyword_gaps ?? [],
+    aiRecommendations: brainstormResult?.ai_recommendations
+      && Object.keys(brainstormResult.ai_recommendations).length > 0
+      ? (brainstormResult.ai_recommendations as AIRecommendations)
+      : null,
+    summary: brainstormResult?.summary
+      && Object.keys(brainstormResult.summary).length > 0
+      ? (brainstormResult.summary as BrainstormSummary)
+      : null,
+    connectGSC,
+    brainstorm,
+    reset,
+  };
+};