Add channel management features and localization support

- Implemented functionality to add new channels with a dialog interface.
- Added validation for channel name and secret inputs, ensuring they meet specified criteria.
- Integrated channel creation logic into the connection provider, including automatic slot assignment and MD5 hashing for channel secrets.
- Updated localization files for multiple languages (Spanish, French, Croatian, Italian, German, Slovenian, and English) to include new channel-related strings.
- Enhanced the contacts tab to display the add channel button conditionally based on device connection status.
- Refactored the contacts tab to improve readability and maintainability.

pubspec.yaml

@@ -96,6 +96,9 @@ dependencies:
   # URL launching
   url_launcher: ^6.3.0
 
+  # Cryptographic functions (for channel secret hashing)
+  crypto: ^3.0.3
+
 dev_dependencies:
   flutter_test:
     sdk: flutter