feat: separate guides into system and custom sections

Add system/custom guide separation with section headers, lock icons,
delete functionality for custom guides, and usage counter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/api/guides/[name]/route.ts

@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
-import { readGuide } from '@/services/guides/guideService';
+import { readGuide, deleteGuide } from '@/services/guides/guideService';
 
 export const runtime = 'nodejs';
 
@@ -25,3 +25,26 @@ export async function GET(
     );
   }
 }
+
+export async function DELETE(
+  _request: NextRequest,
+  { params }: { params: Promise<{ name: string }> }
+) {
+  try {
+    const { name } = await params;
+    const result = deleteGuide(name);
+    if (!result.success) {
+      return NextResponse.json(
+        { success: false, error: result.error },
+        { status: 400 }
+      );
+    }
+    return NextResponse.json({ success: true, message: `Guide "${name}" deleted` });
+  } catch (error) {
+    console.error('[API /guides/[name] DELETE] error:', error);
+    return NextResponse.json(
+      { success: false, error: error instanceof Error ? error.message : 'Failed to delete guide' },
+      { status: 500 }
+    );
+  }
+}