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/network.md

@@ -0,0 +1,72 @@
+# network
+
+**Type:** mxgraph shapes
+**Prefix:** `mxgraph.networks`
+
+## Usage
+
+```xml
+<mxCell value="label" style="shape=mxgraph.networks.server;fillColor=#29AAE1;strokeColor=none;" vertex="1" parent="1">
+  <mxGeometry x="0" y="0" width="60" height="60" as="geometry" />
+</mxCell>
+```
+
+## Shapes (57)
+
+- `biometric_reader`
+- `bus`
+- `business_center`
+- `cloud`
+- `comm_link`
+- `comm_link_edge`
+- `community`
+- `copier`
+- `desktop_pc`
+- `external_storage`
+- `firewall`
+- `gamepad`
+- `hub`
+- `laptop`
+- `load_balancer`
+- `mail_server`
+- `mainframe`
+- `mobile`
+- `modem`
+- `monitor`
+- `nas_filer`
+- `patch_panel`
+- `phone_1`
+- `phone_2`
+- `printer`
+- `proxy_server`
+- `rack`
+- `radio_tower`
+- `router`
+- `satellite`
+- `satellite_dish`
+- `scanner`
+- `secured`
+- `security_camera`
+- `server`
+- `server_storage`
+- `storage`
+- `supercomputer`
+- `switch`
+- `tablet`
+- `tape_storage`
+- `terminal`
+- `unsecure`
+- `ups_enterprise`
+- `ups_small`
+- `usb_stick`
+- `user_female`
+- `user_male`
+- `users`
+- `video_projector`
+- `video_projector_screen`
+- `virtual_pc`
+- `virtual_server`
+- `virus`
+- `web_server`
+- `wireless_hub`
+- `wireless_modem`