perf(web): cache thread plan catalog lookups

[ronak-guliani]

Summary

• Extracts ChatView thread plan catalog selection into a memoized selector in ChatView.logic.ts.
• Reuses the previously resolved environment for stable thread IDs, avoiding repeated cross-environment scans on every ChatView store update.
• Adds a regression test that fails if a stable lookup scans unrelated environments.

Performance audit: 10 candidate improvements

1. apps/web/src/components/ChatView.tsx - cache thread plan catalog environment lookups instead of scanning every environment per requested thread on render. High impact, low effort. Implemented here.
2. apps/web/src/components/Sidebar.tsx - consolidate per-row git status/project subscriptions to reduce visible-row subscription churn. High impact, medium effort.
3. apps/web/src/components/CommandPalette.tsx - keep a stable global keydown listener via refs/effect-event to avoid rebinding on state changes. Medium impact, low effort.
4. apps/web/src/components/DiffPanel.tsx - memoize parsed patch files by patch/scope so large diffs are not reparsed repeatedly. High impact, low effort.
5. apps/web/src/components/chat/MessagesTimeline.logic.ts - collapse repeated timeline derivation passes into one pass and reuse indexes/sets. High impact, medium effort.
6. apps/web/src/components/chat/chatFind.ts - precompute/cache lowercased searchable row text for find-in-chat. Medium impact, low effort.
7. apps/web/src/components/chat/ModelPickerContent.tsx - preindex favorite/model metadata to reduce repeated filtering and tie-break work. Medium impact, low effort.
8. apps/web/src/components/chat/ChangedFilesTree.tsx - avoid traversing the full directory tree to build the expansion reset key on each files update. Medium impact, low effort.
9. apps/web/src/lib/gitStatusState.ts - centralize git status watch fanout so many consumers do not multiply registry/environment subscriptions. High impact, medium effort.
10. apps/web/src/components/WebSocketConnectionSurface.tsx - replace per-second disconnect countdown render loop with a shared/visible-only scheduler. Low impact, low effort.

Validation

• cd apps/web && bun run test src/components/ChatView.logic.test.ts
• bun fmt apps/web/src/components/ChatView.tsx apps/web/src/components/ChatView.logic.ts apps/web/src/components/ChatView.logic.test.ts
• bun lint
• bun typecheck