Slack Agents support: pin QM to the top bar (agent_view) (#572)

* Support Slack Agents (agent_view): pin QM to the top bar with status, titles, and viewing context

Agent split-pane messages already arrive as DM thread messages, so they flow
through the existing DM turn machinery unchanged. This adds the agent_view
manifest feature (+assistant:write scope and the assistant_thread_started /
assistant_thread_context_changed / app_context_changed events) and a small
agent-pane module that layers on the native affordances: a working status
while a turn runs, a thread title from the first message, and a
currently-viewing note passed into the turn context.

Fully backward compatible: installs whose manifest predates the feature never
receive the events, and the first unavailable API response disables the pane
calls for the process. Streaming is left as a marked seam.

Co-Authored-By: QM <qm@ycombinator.com>

* Drop accidentally committed node_modules symlink

* Bump CLI to 0.1.6 (manifest template gains agent_view)

* Sync CLI lockfile version

* fix: address adversarial review findings on agent pane

* fix: untrack node_modules symlink, satisfy oxlint no-useless-spread

* refactor: pin-only Slack agent support

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Co-authored-by: Josh France <josh@ycombinator.com>
Co-authored-by: QM <qm@ycombinator.com>