refactor(file-search): replace heavyweight workspace index

[danielkov]

Summary

Replace fff-search with an in-memory workspace file list built by ignore and fuzzy-matched by neo_frizbee. Prune Git metadata before traversal and report scan failures rather than returning silently incomplete results.

Motivation

Workspace filename search does not need the removed backend's database, Git bindings, or file-watching dependencies. This removes 48 locked packages; both replacement crates remain at their previously locked versions, with no newly selected package versions.

Impact

Search remains capped at 100 results with UTF-8-safe highlighting. Empty queries return alphabetically sorted paths; nonempty queries use the new matcher's ranking and typo tolerance, so result order can differ. Filesystem roots are rejected, and traversal or ignore-rule errors now fail the scan explicitly.

Technical details

File discovery

Walk the workspace in parallel while honoring ignore rules and avoiding symlink traversal. Include hidden files in Git workspaces and exclude .git entries before descent.

Match highlighting

Rank the file list first, then obtain character indices for the top candidates and convert them into merged UTF-8 byte ranges.

[kit-code-agent]

The replacement misinterprets matcher byte offsets as character indices and drops the previous backend's non-Git directory exclusions, causing incorrect highlights and unnecessarily broad workspace scans.

[kit-code-agent]

No issues found. The changes look good to merge.

[kit-code-agent]

No issues found. The changes look good to merge.