Optimize sidebar PR status rerenders

[cursor]

What Changed

• Moved sidebar thread PR/git-status lookup into a small SidebarThreadPrStatusButton child component.
• Removed project cwd plumbing through SidebarProjectThreadList and SidebarThreadRow, so git target updates do not invalidate the whole thread row.
• Added React Scan before/after recordings to the branch:
  • react-scan-recordings/before-sidebar-git-status.webm
  • react-scan-recordings/after-sidebar-git-status.webm

Why

React Doctor and a manual pass identified apps/web/src/components/Sidebar.tsx as a hot path. Each branch thread row owned git-status/project-cwd subscription state, so git target/status changes could rerender the full row. Keeping that subscription in the tiny PR-status child limits the rerender surface to the indicator area.

React Scan was enabled during the recordings. The before recording shows SidebarThreadRow highlights during isolated git-target cwd updates; the after recording shows the same updates no longer highlighting the full rows.

UI Changes

No intended visual UI change.

Before/after React Scan recordings are committed in this PR:

• Before: react-scan-recordings/before-sidebar-git-status.webm
• After: react-scan-recordings/after-sidebar-git-status.webm

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

Verification:

• npx -y react-doctor@latest apps/web --json --offline --fail-on none (initial full scan: score 46/Critical; hot files included Sidebar.tsx, ChatView.tsx, CommandPalette.tsx)
• npx -y react-doctor@latest apps/web --diff main --json --offline --fail-on none (diff scan: score 89/Great on changed file; existing Sidebar diagnostics remain)
• bun fmt
• bun lint (passes; existing warnings emitted)
• bun typecheck

  

Note

Extract PR status rendering into dedicated SidebarThreadPrStatusButton component to reduce rerenders

• Moves git status lookup, PR resolution, and status indicator rendering out of SidebarThreadRow into a new SidebarThreadPrStatusButton component in Sidebar.tsx
• Each thread now derives its own projectCwd from the store via environmentId/projectId, removing the need to pass projectCwd down through SidebarProjectItem → SidebarProjectThreadList → SidebarThreadRow
• The new component only renders when thread.branch is non-null, scoping re-renders to threads with active branches
• Before/after recordings are included in react-scan-recordings/ to validate the rerender reduction

^{Macroscope summarized de766ba.}