test: cover session search fallback on hub timeout and rejection (#13642)

* feat: add searchable session history

Rebased onto main and updated to supersede the sidebar search dialog
from #13533: the sidebar search icon now opens the indexed command bar
(Cmd/Ctrl+P) instead of a sidebar-local cmdk dialog that eagerly loaded
the entire session history via loadAllSessions(). CommandDialog gains a
shouldFilter passthrough so server-ranked FTS hits are displayed as-is.

* fix: harden session history search

* fix: evict failed restoration sessions from search

* fix: preserve deletion when search eviction fails

* fix: address session search review feedback

* fix: preserve search suppression during reconciliation

* test: cover sidecar search fallback on hub timeout and rejection

The existing search_sessions tests only exercised the index-hit and
empty-index-fallback paths with an immediately-resolved hub reply.
Add coverage for the two other realistic Hub-connection failure
modes the fallback is meant to tolerate: the hub call rejecting, and
the hub call hanging past the 750ms withSearchDeadline race.

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Co-authored-by: abeatrix <beatrix@cline.bot>
Co-authored-by: Bee <68532117+abeatrix@users.noreply.github.com>