Deprecate stale sessions

[mattmoran56]

Summary

• Removes the Stale Sessions sidebar section and all supporting state, IPC, app actions, types, mocks, and tests. The feature is superseded by:
  • PR-state grouping in the Sessions section (No PR / Draft PR / Open PR / Merged PR with inline "Clean up").
  • Auto-cleanup on merge (mergedCleanupAction / mergedCleanupDelay).
  • PR sorting (PRSortFilterMenu — number / updated / created).
• Sidebar layout drops from 3/4 panels to 2/3 (Sessions ↔ PRs, or Sessions ↔ Claude Web ↔ PRs when enabled).
• Persisted sessions with a stray staleAt field are loaded back into the unified sessions list automatically — no migration needed.

Screenshots

Sidebar (default — Sessions ↔ Pull Requests, no Stale Sessions panel):

Sidebar with Claude Web enabled (Sessions ↔ Claude Web ↔ Pull Requests):

Full layout:

Test plan

• Screenshots — sidebar in default mode and with Claude Web enabled, confirming no Stale Sessions panel renders.
• npx tsc --noEmit — clean.
• npm run test for tests/unit/stores/sessionStore.test.ts and tests/unit/components/sessions/SessionCard.test.tsx — both pass.
• Manual smoke in npm run dev:
  • Sessions ↔ Pull Requests resize handle works.
  • Toggle Claude Web on; 3-panel layout (Sessions ↔ Claude Web ↔ PRs) with two working resize handles.
  • SessionCard ⋮ menu no longer shows "Mark as stale".
  • In Settings → Custom Buttons, "Mark as Stale" / "Reactivate Session" actions are gone.
  • Merge a PR for an open session — confirm the "Merged PR" group + auto-cleanup still work as the replacement.

🤖 Generated with Claude Code