feat(vpn): improve OpenVPN connection reliability and error handling

- Add detailed logging for VPN stage changes and connection attempts
- Increase connection timeout duration from 45 to 60 seconds
- Enhance error messages with more specific guidance and possible causes
- Validate presence of OpenVPN configuration before attempting connection
- Refactor base64 decoding to try direct decode before normalization fallback
- Add debug output for OpenVPN config sanitization and credential extraction
- Include OpenVPN service declaration and additional VPN permissions in AndroidManifest
- Improve handling of VPN credentials with fallback defaults and config sanitization
- Provide more informative error handling in OpenVpnPort connection logic