docs: add example addon template (#395)

- Create docs/examples/example-addon/ with a complete, copy-paste-ready
  addon skeleton demonstrating command registration, context injection,
  dock panels, lifecycle hooks, and event bus subscription
- Add Examples section to docs/src/SUMMARY.md
- Add quick-start cross-reference in writing-an-addon.md

docs/examples/example-addon/example_addon/__init__.py

@@ -0,0 +1 @@
+"""Example addon for Kindred Create."""

docs/examples/example-addon/example_addon/commands.py

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+"""Example addon commands.
+
+Each command is registered via ``kindred_sdk.register_command()`` which
+wraps FreeCAD's ``Gui.addCommand()`` with input validation.
+"""
+
+from kindred_sdk import register_command
+
+
+def register_commands():
+    """Register all commands for this addon."""
+    register_command(
+        name="ExampleAddon_Hello",
+        activated=_on_hello,
+        resources={
+            "MenuText": "Hello World",
+            "ToolTip": "Show a greeting in the console",
+            # "Pixmap": "path/to/icon.svg",   # optional icon
+            # "Accel": "Ctrl+Shift+H",        # optional shortcut
+        },
+        is_active=lambda: True,
+    )
+
+
+def _on_hello():
+    """Command handler — prints a greeting to the FreeCAD console."""
+    import FreeCAD
+
+    FreeCAD.Console.PrintMessage("Hello from example-addon!\n")

docs/examples/example-addon/example_addon/panel.py

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+"""Example addon dock panel.
+
+The factory function is passed to ``kindred_sdk.register_dock_panel()``
+and called once after the configured delay to create the widget.
+"""
+
+
+def create_panel():
+    """Create the example dock panel widget.
+
+    Must return a QWidget. The widget is embedded in a QDockWidget and
+    managed by FreeCAD's DockWindowManager.
+    """
+    from PySide6 import QtWidgets
+
+    widget = QtWidgets.QWidget()
+    layout = QtWidgets.QVBoxLayout(widget)
+    layout.addWidget(QtWidgets.QLabel("Example Addon Panel"))
+    layout.addWidget(QtWidgets.QLabel("Replace this with your content."))
+    layout.addStretch()
+    return widget