feat(web): pulse running subagents and open their threads in the side panel

[saphid]

What Changed

Subagent rows in the thread details panel's Lineage section now pulse while the agent is actually running, using the repo's stepped status-pulse animation (settled agents keep a steady dot). Each subagent row also gains a split action: clicking the row still navigates to the thread as before, and a new panel button opens the subagent thread as a read-only transcript in the right panel, beside the current conversation instead of replacing it.

The transcript surface is a new right-panel surface kind (thread), rendered from the target thread's projection with every mutating interaction disabled. Scope: web client only. Mobile, desktop shell, wire contracts, and providers are untouched; the server already exposes everything the client needs.

Why

Subagent lineage rows had exactly one behavior: replace the current thread. Watching what a subagent is doing meant losing your place in the parent conversation. The pulse closes the opposite gap: a settled dot and a running dot looked identical, so you couldn't tell at a glance whether the fleet was still working. This builds on the lineage panel from agent/web-subagent-lineage and follows its existing split-row pattern (the same one the merge-back button uses).

Verification

• pnpm --filter @t3tools/web run typecheck: passed (no errors; only pre-existing effect-schema suggestions in unrelated files).
• vp test run src/rightPanelStore.test.ts src/components/chat/ThreadTranscriptPanel.test.tsx src/components/chat/ThreadRelationshipsControl.agents.test.tsx in apps/web: 69 passed, 0 failed. New tests cover: thread surface dedupe/title refresh/scoping/closing, loading persisted panels from versions without thread surfaces, the open-in-panel action wiring and its callback, and rows staying single-button when the callback is absent.
• Exercised in a running client against an isolated dev home: drove a real turn that delegated a subagent, confirmed the live row renders animate-status-pulse while running, clicked "Open in side panel" and confirmed the read-only transcript beside the thread, then re-verified the before state by temporarily stashing the diff against the same session.

UI Changes

Before — lineage rows navigate only, static dots:

After — split rows with an open-in-panel action:

After — subagent thread open as a read-only transcript beside the conversation:

Motion — running subagent's dot pulsing in the Lineage panel (MP4):

running-pulse video (MP4)

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Implementation used GLM xlarge via OpenCode in T3 Code.

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for 38fff38.

This comment will update automatically after the next completed run.