Update media-server: Add execution timing and improve script/callback execution UI

Backend improvements:
- Add execution_time tracking for script execution
- Add execution_time tracking for callback execution
- Add /api/callbacks/execute/{callback_name} endpoint for debugging callbacks

Frontend improvements:
- Fix duration display showing N/A for fast scripts (0 is falsy in JS)
- Increase duration precision to 3 decimal places (0.001s)
- Always show output section with "(no output)" message when empty
- Improve output formatting with italic gray text for empty output

Documentation:
- Add localization section to README
- Document available languages (English, Russian)
- Add guide for contributing new translations

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

README.md

@@ -29,6 +29,7 @@ The media server includes a built-in web interface for controlling and monitorin
 - **Token authentication** - Saved in browser localStorage
 - **Responsive design** - Works on desktop and mobile
 - **Dark theme** - Easy on the eyes
+- **Multi-language support** - English and Russian locales with automatic detection
 
 ### Accessing the Web UI
 
@@ -56,6 +57,38 @@ To access the Web UI from other devices on your network:
 
 **Security Note:** For remote access over the internet, use a reverse proxy with HTTPS (nginx, Caddy) to encrypt traffic.
 
+### Localization
+
+The Web UI supports multiple languages with automatic browser locale detection:
+
+**Available Languages:**
+
+- **English (en)** - Default
+- **Русский (ru)** - Russian
+
+The interface automatically detects your browser language on first visit. You can manually switch languages using the dropdown in the top-right corner of the Web UI.
+
+**Contributing New Locales:**
+
+We welcome translations for additional languages! To contribute a new locale:
+
+1. Copy `media_server/static/locales/en.json` to a new file named with your language code (e.g., `de.json` for German)
+2. Translate all strings to your language, keeping the same JSON structure
+3. Add your language to the `supportedLocales` object in `media_server/static/index.html`:
+
+   ```javascript
+   const supportedLocales = {
+       'en': 'English',
+       'ru': 'Русский',
+       'de': 'Deutsch'  // Add your language here
+   };
+   ```
+
+4. Test the translation by switching to your language in the Web UI
+5. Submit a pull request with your changes
+
+See [CLAUDE.md](CLAUDE.md#internationalization-i18n) for detailed translation guidelines.
+
 ## Requirements
 
 - Python 3.10+