fix(showcase/ms-agent-python): repair stale chat-slots and headless-complete highlights

Both manifest entries point at file names that no longer exist on disk
after the LGP-cells port (PR CopilotKit#4895). The bundler errors at build time
on the missing paths, which blocked PR CopilotKit#4900's shell rebuild.

Adopt LGP's canonical highlight pattern for both demos.

- chat-slots: drop the three custom-* refs, keep page.tsx + slot-wrappers.tsx
- headless-complete: drop message-list.tsx + use-rendered-messages.tsx,
  add the chat/, hooks/, attachments/ subpaths that LGP uses

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

Author: marthakelly

showcase/integrations/ms-agent-python/manifest.yaml

@@ -281,9 +281,7 @@ demos:
     highlight:
       - src/agents/agent.py
       - src/app/demos/chat-slots/page.tsx
-      - src/app/demos/chat-slots/custom-welcome-screen.tsx
-      - src/app/demos/chat-slots/custom-assistant-message.tsx
-      - src/app/demos/chat-slots/custom-disclaimer.tsx
+      - src/app/demos/chat-slots/slot-wrappers.tsx
       - src/app/api/copilotkit/route.ts
   - id: headless-simple
     name: Headless Chat (Simple)
@@ -306,8 +304,11 @@ demos:
     highlight:
       - src/agents/agent.py
       - src/app/demos/headless-complete/page.tsx
-      - src/app/demos/headless-complete/message-list.tsx
-      - src/app/demos/headless-complete/use-rendered-messages.tsx
+      - src/app/demos/headless-complete/chat/chat.tsx
+      - src/app/demos/headless-complete/hooks/use-tool-renderers.tsx
+      - src/app/demos/headless-complete/hooks/use-frontend-components.ts
+      - src/app/demos/headless-complete/hooks/use-headless-suggestions.ts
+      - src/app/demos/headless-complete/attachments/use-attachments-config.ts
       - src/app/api/copilotkit/route.ts
   - id: agentic-chat-reasoning
     name: Reasoning