feat: Forge Workspaces section in landing page
Replaces the simple smart folder with a dedicated Forge Workspaces
section showing individual workspace cards with:
- Decrypted workspace title (2-line clamp)
- Type badge (workspace vs report)
- Relative timestamp (2h ago, 3d ago)
- Version count badge (async fetched)
- Latest version label (e.g., "Final evaluation")
Shows both forge-workspace and forge-report tagged docs, sorted by
most recently updated. Section only appears at root level.