feat(gtm): Implement Rich Session Browser UI

- Replaced the basic session list with a dedicated, card-based Session Browser page.
- Each session card now displays product name, category, description, and a thumbnail placeholder for better usability.
- Updated the backend DB manager to extract this rich information from the existing JSON data store.
- Refactored the frontend (App.tsx, types.ts) to support the new UI and data structure.
- Added new component SessionBrowser.tsx and its corresponding CSS.
- Updated documentation to reflect the v2.6 changes.

gtm-architect/types.ts

@@ -165,4 +165,8 @@ export interface ProjectHistoryItem {
     name: string;
     created_at: string;
     updated_at: string;
+    productName: string;
+    productCategory: string;
+    productDescription: string;
+    productThumbnail?: string; // Optional for now
 }