feat(client): add a search box to the revision selector

[yoshiko-pg]

Summary

Implements suggestion 2 from #432: a searchable branch/commit picker.

Quick menu (main dropdown)

• A sticky filter input now sits at the top of the revision quick menu, above the Quick Diffs section.
• Typing filters across:
  • Quick Diff presets (HEAD, HEAD...Uncommitted, main...Uncommitted, Previous commit, ...)
  • Recent commits — selecting one shows commit^...commit
  • Branches — selecting one shows branch...Uncommitted (merge-base), consistent with the existing presets
• Pressing Enter selects the first match; an empty state is shown when nothing matches. The query resets when the menu closes.

Detailed Diff selector

• The Base/Target revision dropdowns in the Detailed Diff modal get the same filter input (focused on open, Enter selects the first enabled match).
• The dropdown height is now capped with floating-ui's size middleware so the list always fits inside the viewport. Previously it could overflow off-screen when it flipped upward.

Test plan

• Unit tests for quick menu filtering (presets/commits/branches), commit and branch selection semantics, Enter-selects-first-match, empty state
• Unit tests for the Detailed selector filtering
• Verified in the browser with pnpm run dev: typing inline in the quick menu narrows to the matching commit and the feat/inline-reply-box branch

Part of #432

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