fix(hub): refresh session activity on completed turns

[Liu-KM]

Summary

Fix stale session ordering in the sidebar by refreshing sessions.updated_at when a conversation has real user-visible activity.

Root Cause

Session summaries are sorted from sessions.updated_at, but message writes did not update that field. A session could receive new messages while its sidebar timestamp stayed at the original session metadata update time.

Fix

• Add a store/cache path for touching session activity and publishing session-updated.
• Refresh activity when the web app sends a user message.
• Refresh activity from the CLI socket only for real user text input and the ready event that marks a completed turn.
• Do not refresh activity for intermediate agent/tool messages such as tool calls, tool results, reasoning, or terminal output.

Validation

• bun test hub/src/sync/sessionModel.test.ts
• bun run typecheck from hub
• bun run test from hub

No dependency or lockfile changes.

[github-actions]

Findings
None.

Summary
Review mode: initial
No issues found in the latest diff. Residual risk: static review only; tests were not run in this automation pass.

Testing
Not run (automation)

HAPI Bot