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/sitemap.md

@@ -0,0 +1,68 @@
+# sitemap
+
+**Type:** mxgraph shapes
+**Prefix:** `mxgraph.sitemap`
+
+## Usage
+
+```xml
+<mxCell value="label" style="shape=mxgraph.sitemap.{shape};fillColor=#7ea6e0;strokeColor=#6c8ebf;" vertex="1" parent="1">
+  <mxGeometry x="0" y="0" width="60" height="60" as="geometry" />
+</mxCell>
+```
+
+
+
+## Shapes (51)
+
+- `about_us`
+- `audio`
+- `biography`
+- `blog`
+- `calendar`
+- `chart`
+- `chat`
+- `cloud`
+- `contact`
+- `contact_us`
+- `document`
+- `download`
+- `error`
+- `faq`
+- `form`
+- `gallery`
+- `game`
+- `home`
+- `info`
+- `jobs`
+- `log`
+- `login`
+- `mail`
+- `map`
+- `mxgraph.sitemap`
+- `news`
+- `page`
+- `payment`
+- `photo`
+- `portfolio`
+- `post`
+- `pricing`
+- `print`
+- `products`
+- `profile`
+- `references`
+- `script`
+- `search`
+- `security`
+- `services`
+- `settings`
+- `shopping`
+- `sitemap`
+- `slideshow`
+- `sports`
+- `success`
+- `text`
+- `upload`
+- `user`
+- `video`
+- `warning`