feat: add UV runtime support in manifest v0.4

Add UV as a new server type for Python extensions that use UV runtime
for dependency management instead of bundling dependencies.

Schema changes (v0.4):
- Add "uv" to server.type enum
- Make mcp_config optional (not needed for UV type)
- UV extensions rely on pyproject.toml for dependencies

Documentation:
- Add UV runtime section to MANIFEST.md explaining benefits and usage
- Update README.md to recommend UV runtime for Python
- Add complete hello-world-uv example

Benefits of UV runtime:
- Cross-platform support (Windows/macOS/Linux, Intel/ARM)
- Small bundle size (~100 KB vs 5-10 MB)
- Handles compiled dependencies portably
- No user Python installation required

Example manifest:
{
  "manifest_version": "0.4",
  "server": {
    "type": "uv",
    "entry_point": "src/server.py"
  }
}

Co-authored-by: Joan <joan@anthropic.com>

examples/hello-world-uv/src/server.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""Hello World MCP server using UV runtime."""
+
+import asyncio
+from mcp.server.models import InitializationOptions
+import mcp.types as types
+from mcp.server import NotificationOptions, Server
+import mcp.server.stdio
+
+
+server = Server("hello-world-uv")
+
+
+@server.list_tools()
+async def handle_list_tools() -> list[types.Tool]:
+    """List available tools."""
+    return [
+        types.Tool(
+            name="say_hello",
+            description="Say hello to someone",
+            inputSchema={
+                "type": "object",
+                "properties": {
+                    "name": {
+                        "type": "string",
+                        "description": "Name to greet",
+                    }
+                },
+                "required": ["name"],
+            },
+        )
+    ]
+
+
+@server.call_tool()
+async def handle_call_tool(
+    name: str, arguments: dict | None
+) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+    """Handle tool calls."""
+    if name == "say_hello":
+        person_name = arguments.get("name", "World") if arguments else "World"
+        return [types.TextContent(type="text", text=f"Hello, {person_name}!")]
+
+    raise ValueError(f"Unknown tool: {name}")
+
+
+async def main():
+    """Run the server."""
+    async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
+        await server.run(
+            read_stream,
+            write_stream,
+            InitializationOptions(
+                server_name="hello-world-uv",
+                server_version="1.0.0",
+                capabilities=server.get_capabilities(
+                    notification_options=NotificationOptions(),
+                    experimental_capabilities={},
+                ),
+            ),
+        )
+
+
+if __name__ == "__main__":
+    asyncio.run(main())