Refine codgrep integration boundaries and workspace search UI

[wgqqqqq]

Summary

This PR cleans up the BitFun <-> codgrep boundary and updates the workspace search UI/status flow.

Changes

• refine BitFun search service to rely on the codgrep SDK-managed runtime boundary
• remove host-specific .bitfun assumptions from vendored codgrep internals
• update vendored codgrep README/docs to match the current code and SDK-first integration story
• normalize workspace search backend/status/task types into BitFun-owned API types
• expose workspace search status in the desktop/web UI and move index actions to the workspace list indicator

Validation

• cargo check -p bitfun-core -p codgrep
• cargo test -p codgrep workspace_internal_path_detects_codgrep_artifacts
• cargo test -p codgrep scan_paths_excludes_codgrep_internal_files_and_configured_index_path
• cargo check -p bitfun-desktop
• pnpm exec tsc --noEmit

Notes

• vendored codgrep changes are intended to keep the library third-party friendly for future SDK exposure
• this PR is opened as draft for review of the integration boundary and vendored dependency strategy first