feat(ui): add skills pane in left nav and wire skills api/service

app/api/skills/route.ts

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