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>

src/components/settings/ContextViewer.tsx

@@ -73,7 +73,7 @@ export default function ContextViewer() {
   return (
     <div style={containerStyle}>
       <p style={descStyle}>
-        Top 10 most-connected nodes are added to background context for workflow execution.
+        Top 10 most-connected nodes are added to background context for tool execution.
       </p>
 
       {/* Toggle */}