Force a freshness check each time the user enters the Checks tab
(open sidebar, switch to Checks tab, or switch active worktree/branch)
so stale PR metadata, cached-null "no PR" results, stale checks, and
stale comments are surfaced immediately rather than waiting for the
cache TTL.
- Extracts entry-refresh logic into `checks-entry-refresh.ts` with a
30 s grace window to suppress rapid show/hide duplicate fetches.
- Adds a `shouldEntryRefresh` effect in `ChecksPanel` keyed by
`activeWorktreeId::repo.path::branch`; resets on panel hide so
close-and-reopen re-evaluates freshness.
- Fixes a stale-closure bug in `handleRefresh`: `fetchPRChecks` is now
called directly with the freshly resolved `headSha` after PR refresh
instead of reusing the pre-refresh closure's captured sha.
- Adds 11 unit tests in `checks-entry-refresh.test.ts`.
- Design doc: `docs/refresh-on-checks-tab.md`.
Co-authored-by: Orca <help@stably.ai>
