Fix ExpoAVVideoAdapter error handling - provide clear guidance when expo-av missing

Problem: Video adapters show vague "expo-av/expo-video is not available" errors when dependencies are missing, causing developer confusion during setup.

Current: Generic error messages with no installation guidance or resolution steps.

Expected: Clear, actionable errors like "ExpoAVVideoAdapter: Module not found. Please install expo-av: 'npx expo install expo-av'"

Impact: Affects all platforms during initial setup - wastes developer time and creates unnecessary support issues.

Solution: Implement getAvailabilityInfo() method with detailed error context and installation commands.

## Is the issue reproducible only on a specific device?
[✓ ] No
[ ] Yes (specify device model + iOS/Android version)
This is a dependency issue - affects all devices when expo-av isn't installed

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