Fix X bot synthesis functionality with custom implementation
- Replace import of send_synthesis_message from bsky.py with custom send_x_synthesis_message function
- Create X-specific synthesis prompt focusing on X/Twitter platform experiences
- Use simplified Letta client message creation instead of streaming for X synthesis
- Remove dependency on atproto_client and bsky context that was causing 'NoneType' errors
- Add proper error handling in X synthesis function
X bot synthesis now works independently without bsky.py dependencies.
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Co-Authored-By: Claude <noreply@anthropic.com>