Add platform-specific tool management system
- Creates tool_manager.py to automatically switch between Bluesky and X tools
- Updates bsky.py and x.py to configure appropriate tools on startup
- Fixes CLIENT.agents.get() API call to use agents.retrieve()
- Adds TOOL_MANAGEMENT.md documentation
- Ensures platform isolation: X tools only for x.py, Bluesky tools only for bsky.py
- Common tools (webpage, halt, etc.) remain available on both platforms
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Co-Authored-By: Claude <noreply@anthropic.com>