Previously, search_files would silently return 0 results when the
search path didn't exist (e.g., /root/.hermes/... when HOME is
/home/user). The path was passed to rg/grep/find which would fail
silently, and the empty stdout was parsed as 'no matches found'.
Changes:
- Add path existence check at the top of search() using test -e.
Returns SearchResult with a clear error message when path doesn't exist.
- Add exit code 2 checks in _search_with_rg() and _search_with_grep()
as secondary safety net for other error types (bad regex, permissions).
- Add 4 new tests covering: nonexistent path (content mode), nonexistent
path (files mode), existing path proceeds normally, rg error exit code.
Tests: 37 → 41 in test_file_operations.py, full suite 2330 passed.
These tests documented the macOS symlink bypass bug with
platform-conditional assertions. The fix and proper regression
tests are in PR #61 (tests/tools/test_write_deny.py), so remove
them here to avoid ordering conflicts between the two PRs.
