fix(find): prevent silent false negatives

[coyaSONG]

Summary

• Preserve explicit file and directory roots instead of dropping their empty relative path.
• Treat a lone existing RTK-syntax argument as the search root, and preserve native find visibility for hidden and gitignored entries.
• Print an explicit zero-match result so a successful search cannot be mistaken for missing data.

Closes #2995.

Root cause and impact

The walker stripped the search root from every result and discarded the resulting empty path, so an explicitly requested file or directory disappeared. RTK syntax also treated a lone existing path as a basename glob, while native-flag syntax still applied RTK's ignore-aware pruning. Finally, the zero-result branch returned without output. Together these paths produced silent false negatives with exit code 0.

Native-flag syntax now disables hidden and ignore-file pruning, while compact RTK syntax retains its existing pruning behavior. An explicit second positional search root still wins over path auto-detection, preserving inputs such as rtk find . src.

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk find ./journal.md -type f, bare file roots, directory roots, native hidden/gitignored matches, compact pruning, and zero-match output inspected

The full suite passed with 2,437 unit tests and all integration test binaries green (8 tests ignored by the repository).

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