test(tools): add coverage for ListFilesTool, SearchFilesTool, ApplyPatchTool; improve ReadFileTool (#169)

Add dedicated test suites for workspace-boundary symlink resolution
coverage to close the codecov/patch gap:

- New: listFilesTool.spec.ts (13 tests) — listing, approval, boundary, handlePartial
- New: searchFilesTool.spec.ts (12 tests) — search, approval, boundary, handlePartial
- New: applyPatchTool.spec.ts (23 tests) — execute, validation, approval, boundary
- Improved: readFileTool.spec.ts (+15 tests) — legacy format, handlePartial, error paths

All 96 tests pass. tsc --noEmit clean.

Author: proyectoauraorg