feat: add get_shape_library tool for AI icon discovery (#335)

* 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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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

docs/shape-libraries/lean_mapping.md

@@ -0,0 +1,31 @@
+# lean_mapping
+
+**Type:** mxgraph shapes
+**Prefix:** `mxgraph.lean_mapping`
+
+## Usage
+
+```xml
+<mxCell value="label" style="shape=mxgraph.lean_mapping.{shape};strokeWidth=2;" vertex="1" parent="1">
+  <mxGeometry x="0" y="0" width="60" height="60" as="geometry" />
+</mxCell>
+```
+
+
+
+## Shapes (14)
+
+- `airplane_7`
+- `electronic_info_flow`
+- `finished_goods_to_customer`
+- `go_see_production_scheduling`
+- `kaizen_lightening_burst`
+- `kanban_post`
+- `load_leveling`
+- `manual_info_flow`
+- `move_by_forklift`
+- `mrp_erp`
+- `mxgraph.lean_mapping`
+- `operator`
+- `quality_problem`
+- `verbal`