Add MCP Apps extension support (typed metadata, attribute, and helpers) (#1484)

samples/WeatherAppServer/README.md

@@ -0,0 +1,41 @@
+# Weather App Server
+
+An MCP server that demonstrates the **MCP Apps** extension by serving an interactive weather forecast UI alongside weather tools.
+
+## What it shows
+
+- **`[McpAppUi]` attribute** — declaratively associates a UI resource with a tool
+- **`WithMcpApps()`** — builder extension that processes `[McpAppUi]` attributes
+- **UI resource** — an HTML page served via `McpServerResource` with MIME type `text/html;profile=mcp-app`
+- **Structured content** — tool results include `StructuredContent` for the UI to render
+
+## Running
+
+```bash
+dotnet run
+```
+
+The server starts on `http://localhost:5000` by default. Connect any MCP Apps-capable client to the `/mcp` endpoint.
+
+Then prompt that will cause the LLM to request the use of the "weather_ui" tool.
+A general prompt like "What's the weather?" will probably work, but if not you could try explicitly requesting the tool
+with something like "@weather_ui". This should load the Weather App UI in an iFrame that you can then interact with
+to get the weather forecast for a number of US cities.
+
+![UI of the Weather Forecast MCP App in VS Code](./WeatherUI.png)
+
+## Tools
+
+| Tool | Description |
+|------|-------------|
+| `weather_ui` | Opens the weather forecast UI |
+| `weather_forecast` | Gets a multi-period forecast from the National Weather Service for a US city |
+
+Both tools are linked to the `ui://weather-app/forecast` resource via the `[McpAppUi]` attribute.
+
+## Resources
+
+| URI | Description |
+|-----|-------------|
+| `ui://weather-app/forecast` | Interactive weather forecast HTML UI |
+| `data://weather-app/us-cities` | JSON list of supported US cities |