* feat: add get_shape_library tool for AI icon discovery
- Add server-side tool that returns shape library documentation
- AI can fetch icon/shape names on-demand before generating diagrams
- Includes path traversal protection and input sanitization
- Library index embedded in tool description for discoverability
- Supports 33 libraries: AWS, Azure, GCP, Kubernetes, Cisco, etc.
* fix: improve get_shape_library error handling and imports
- Move fs/path imports to top of file (avoid dynamic imports per call)
- Distinguish file-not-found vs other errors in catch block
- Include invalid input in validation error message
- Log unexpected errors for debugging
* docs: add get_shape_library to system prompt tool list
- Add Tool4 (get_shape_library) to available tools section
- Add usage guidance in 'Choose the right tool' section
- Update AWS icons note to reference get_shape_library for icon discovery
* fix: display get_shape_library tool output in chat UI
* fix: correct state check for get_shape_library output display
* fix: make get_shape_library output respect fold state
* style: auto-format with Biome
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