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/electrical.md

@@ -0,0 +1,50 @@
+# electrical
+
+**Type:** mxgraph shapes
+**Prefix:** `mxgraph.electrical`
+
+## Usage
+
+```xml
+<mxCell value="label" style="shape=mxgraph.electrical.resistors.resistor_1;" vertex="1" parent="1">
+  <mxGeometry x="0" y="0" width="60" height="20" as="geometry" />
+</mxCell>
+```
+
+Shapes are organized by category: `mxgraph.electrical.{category}.{shape}`
+
+## Categories
+
+### resistors
+- `resistor_1`
+- `resistor_2`
+
+### capacitors
+- `capacitor_1`
+- `capacitor_3`
+
+### inductors
+- `inductor_3`
+- `transformer_1`
+
+### diodes
+- `diode`
+- `zener_diode_1`
+
+### transistors
+- `npn_transistor_1`
+- `pnp_transistor_1`
+
+### mosfets1
+- `n-channel_mosfet_1`
+- `p-channel_mosfet_1`
+
+### logic_gates
+- `logic_gate`
+- `dual_inline_ic`
+
+### electro-mechanical
+- `singleSwitch`
+- `pushbutton`
+
+(See draw.io Electrical shape library for complete list)