feat(rn): [P0] Agent activity timeline (tool/file_edit) #4

Summary

Upgrade from one-line tool progress to a collapsible activity cluster: tool_hint / progress / file_edit. Skip image evidence for MVP.

WebUI reference

• webui/src/components/thread/AgentActivityCluster.tsx
• webui/src/hooks/sessions/useMinibotStream.ts
• webui/src/hooks/sessions/streamFileEdits.ts
• webui/src/lib/types/protocol.ts

RN existing

• src/lib/minibot/wsTurn.ts
• src/components/chat/ToolProgressCard.tsx
• src/components/chat/ChatBubble.tsx
• (tabs)/index.tsx onToolProgress

RN landing

• Extend wsTurn.ts for file_edit
• New AgentActivityCard.tsx (or upgrade ToolProgressCard)
• Render via ChatBubble

Acceptance

• Tool name/phase visible during turn
• file_edit shows path when available
• Coexists with existing ApprovalCard HITL

Depends

None (parallel with Models)