Add key mutation commands (add, set, unset, delete) for v0.0.4

- Add CLI commands: add, set, unset, delete for modifying .env files
- Add value auto-quoting for special characters (spaces, #, quotes, newlines)
- Add example file detection with warning for .env.example/.sample/.template
- Add library API: addEnvFileKey, setEnvFileKey, unsetEnvFileKey, deleteEnvFileKeys
- Export isExampleEnvFile utility
- Add tests for new mutation operations
- Update README and CHANGELOG

CHANGELOG.md

@@ -4,6 +4,27 @@ All notable changes to this project are documented in this file.
 
 This project follows [Semantic Versioning](https://semver.org/) and the format is loosely based on [Keep a Changelog](https://keepachangelog.com/).
 
+## 0.0.4 (2026-01-15)
+
+### Added
+
+- Key mutation commands (CLI): `add`, `set`, `unset`, `delete`.
+  - `add`: Add a new key-value pair (fails if key already exists).
+  - `set`: Create or update a key-value pair (idempotent).
+  - `unset`: Set a key's value to empty (`KEY=`).
+  - `delete`: Remove key(s) from the file entirely (supports `--keys` for multiple).
+- Value auto-quoting: Values with spaces, `#`, quotes, newlines, or other special characters are automatically double-quoted with proper escaping.
+- Example file detection: Warns when targeting `.env.example`, `.env.sample`, `.env.template`, `.env.dist`, `.env.default(s)` files. Suppressible with `--no-example-warning`.
+- Library API exports for key mutations: `addEnvFileKey`, `setEnvFileKey`, `unsetEnvFileKey`, `deleteEnvFileKeys`.
+- Utility export: `isExampleEnvFile` for detecting example/template env files.
+- Test coverage for new mutation operations.
+
+### Changed
+
+- Package version bumped to `0.0.4`.
+- Updated CLI help text to include new commands and notes about dry-run behavior.
+- Updated README with documentation for new commands and library API.
+
 ## 0.0.3 (2026-01-13)
 
 ### Added