fix(gtm): Fix white screen and implement URL persistence v2.6.1

- Fixed TypeError in SessionBrowser by adding defensive checks for the sessions array.
- Implemented mandatory URL persistence: The research URL is now saved in DB, shown in UI, and included in reports.
- Added 'Start New Analysis' button to the session browser for better UX flow.
- Updated documentation to reflect v2.6.1 changes.

gtm-architect/types.ts

@@ -168,5 +168,6 @@ export interface ProjectHistoryItem {
     productName: string;
     productCategory: string;
     productDescription: string;
+    sourceUrl: string;
     productThumbnail?: string; // Optional for now
 }