docs, test: add config management documentation and tests

README.md

@@ -52,6 +52,9 @@ Options:
   --[no-]copy    Copy result to clipboard
   --[no-]notify  Show desktop notification
   --desktop      GUI mode: pick → copy → notify
+  --get-config   Print the current configuration
+  --set-config   Update the configuration (e.g. --set-config desktop --copy)
+  --reset-config Restore the configuration file to its default values
   --install      Install to ~/.local/share/ and symlink to ~/.local/bin/
   --help, -h     Show this help message
 ```
@@ -102,6 +105,22 @@ copy   = true   # copy result to clipboard
 notify = true   # show desktop notification with the copied value
 ```
 
+You can also use the CLI to manage your configuration:
+
+```bash
+# View current config
+color-tool --get-config
+
+# Update specific keys (e.g., enable swatch by default)
+color-tool --set-config defaults --swatch
+
+# Set output format for desktop mode
+color-tool --set-config desktop output=rgba
+
+# Reset to factory defaults
+color-tool --reset-config
+```
+
 ## 🧪 Testing
 
 The project includes a comprehensive test suite that verifies color conversion, configuration loading, and system integrations (clipboard/notifications) using mocks.