feat(tui): move search to background worker with deferred filters

[samzong]

What's changed?

• Move TUI search off the main thread into a background SearchWorker that runs text search first, then semantic refinement
• Defer filter edits until Esc applies them, using draft state for source, project, time range, and sort
• Track search request IDs to ignore stale responses when typing quickly
• Show inline search feedback in the query box (queued, searching, refining semantic)
• Increase search debounce to 250ms

Why

• Hybrid text+semantic search was blocking the TUI event loop, making typing and navigation feel sluggish
• Filter tweaks previously triggered immediate re-searches; deferring until Esc keeps the filter panel usable without redundant work

Verification

• cargo test — 247 tests passed (192 unit, 7 CLI, 5 eval harness, 43 regression)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Invalidate in-flight searches when applying filters

When filters are applied while a previous search for the same query is still in flight, close_filters updates the active filters but only queues a debounced replacement search; until that new request is sent, this guard still accepts the old response because it only compares request id and query text. That can briefly replace the list with results from the old source/project/time scope under the new filter bar, and a quick Enter can open a session outside the selected filters; invalidate the active request or include the filter snapshot in the staleness check when filters change.

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