perf(frontend): abort and cache search requests

[Flickwire-Agent]

Summary

Abort in-flight search requests and cache repeated query results client-side.

Evidence

• Search debounce fetches without AbortController at apps/web/src/components/SearchBox.tsx:21 to apps/web/src/components/SearchBox.tsx:42.

Expected Impact

Low to medium. Improves typing responsiveness and avoids stale responses overriding newer searches.

Implementation Notes

Normalize search keys by trimming/lowercasing. Add a small TTL cache and abort the previous request on query change.

Acceptance Criteria

• Older search responses cannot overwrite newer query results.
• Repeating a recent search does not hit the network.