feat(android): add SMS-triggered incoming call support

[ivan-bilchenko]

Description

Adds support for triggering incoming VoIP calls on Android via specially formatted SMS messages, serving as a fallback mechanism when push notifications are unavailable or unreliable.

Main additions:

• New API to configure SMS prefix and ICU-compatible regex from Flutter side
• Android BroadcastReceiver to intercept SMS and parse metadata using regex
• Sample ADB command for testing incoming SMS
• Updated documentation:
• README.md: usage instructions and examples
• docs/sms_trigger_regex_requirements.md: formal regex spec and examples
• performReceivedCall() method now supports displayName

⚠️ Security note: The SMS trigger only activates if the message starts with a trusted prefix and matches a strict regex with four capture groups (callId, handle, displayName, hasVideo), which helps meet Play Store policies.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore