Fix X mention username resolution and add user ID mapping
**Fixes the '@unknown (unknown)' issue:**
- Added fallback username resolution when thread_data['users'] lookup fails
- Scans thread tweets to find author info when primary lookup returns 'unknown'
- Logs successful fallback resolutions
**Added User ID Mapping Key:**
- Builds comprehensive user_id → @username mapping from thread data
- Appends USER_ID_KEY section to prompts showing all participants
- Helps void understand who is who when user IDs appear without handles
**Example output:**
```
USER_ID_KEY:
1232326955652931584: @cameron_pfiffer
1188460292998602752: @scholzmx
1950680610282094592: @void_comind
```
This resolves cases where the X API doesn't consistently provide usernames in mention data, using the thread context as a reliable fallback source.
🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>