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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "envsitter",
-  "version": "0.0.3",
+  "version": "0.0.4",
   "private": false,
   "type": "module",
   "description": "Safely inspect and match .env secrets without exposing values",