feat: v0.2.0 optimization refactor and docs

- Refactor core traversal to single-pass O(N) tree construction
- Optimize CSV output using `csv` crate for robust escaping
- Optimize JSON output with zero-copy serialization
- Add MANUAL.md
- Bump version to 0.2.0
- Remove walkdir dependency

CHANGELOG.md

@@ -5,6 +5,19 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.0] - 2026-01-22
+
+### Changed
+- Refactored core traversal logic to a **single-pass, in-memory tree construction** algorithm. This visits every file exactly once, replacing the previous $O(N \times Depth)$ behavior with $O(N)$.
+- Switched default CSV output to use the `csv` crate for robust escaping (fixes issues with filenames containing commas).
+- Optimized JSON output to use zero-copy serialization, improving performance and memory usage.
+
+### Added
+- Added `MANUAL.md` with comprehensive usage documentation.
+
+### Removed
+- Removed `walkdir` dependency (replaced by `ignore::WalkBuilder` for all traversal).
+
 ## [0.1.0] - 2026-01-22
 
 ### Added