Mobile: show checks, review and watch state for linked pull requests, like desktop #20212

Requesting agreement on direction and scope before I write any code.

• Problem: When an agent watches pull requests, the phone shows only a "Waiting on N monitors" pill, which cannot be tapped. The linked pull requests list at the bottom of the Git sheet shows "open · Watching" for each one, with no checks or review state. On desktop, the thread's pull requests panel shows a checks glyph and a review decision glyph on each row, and its menu has Watch for changes / Stop watching. From a phone I cannot see which watched PR is failing or approved, or stop or start a watch.
• Proposal: On each mobile linked pull request row, show the same checks and review decision state as desktop (snapshot.checksState, snapshot.reviewDecision), and add Watch / Stop watching, gated on capabilities.threadPullRequestWatch like the web panel. Optionally, tapping the monitors pill opens the thread's linked pull requests list.
• Scope: Mobile only. It reuses the existing snapshot data and the existing watch commands. No server or contract changes.
• Related: @flamboh's stack (refactor(mobile): pick pull request glyphs from one module #20189 to feat(mobile): open pull requests with conflicts show a warning like web #20192) adds a Linked pull requests sheet with state and conflict glyphs. It does not show checks, review or watch controls. I would build on its shared LinkedPullRequestChains row after it merges, so the two do not conflict. feat(mobile): stop leftover background work from the status pill #18287 makes the status pill tappable to stop background work, so the pill part may fit there instead.

Would you approve the row glyphs and the watch toggle as scope? Is the pill tap wanted, or should I leave it out?