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>

app/api/guides/route.ts

@@ -0,0 +1,17 @@
+import { NextResponse } from 'next/server';
+import { listGuides } from '@/services/guides/guideService';
+
+export const runtime = 'nodejs';
+
+export async function GET() {
+  try {
+    const guides = listGuides();
+    return NextResponse.json({ success: true, data: guides });
+  } catch (error) {
+    console.error('[API /guides] error:', error);
+    return NextResponse.json(
+      { success: false, error: error instanceof Error ? error.message : 'Failed to list guides' },
+      { status: 500 }
+    );
+  }
+}