feat(rah-light): replace workflows with guides system

- Remove entire workflow system (API routes, services, tools, components)
- Add guides system from main ra-h repo (for external agent integration)
- Update pane types: 'workflows' → 'guides' throughout
- Update LeftToolbar to show guides icon instead of workflows
- Update SettingsModal with GuidesViewer tab
- Add GuidesPane for browsing guides in main UI
- Clean up prompts to remove workflow references
- Update tool registry to remove workflow tools
- Add gray-matter package for frontmatter parsing

Guides are essential for RA-H Light as they help external agents
(via MCP) understand the knowledge base context and usage patterns.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -28,6 +28,7 @@
     "ai": "^6.0.27",
     "better-sqlite3": "^12.2.0",
     "cheerio": "^1.1.2",
+    "gray-matter": "^4.0.3",
     "lucide-react": "^0.468.0",
     "next": "15.1.3",
     "openai": "^4.103.0",