feat(server): add --transport option and STDIO mode to Program.cs

[CalvinAllen]

Parent Epic

Part of #18 - STDIO Transport Support

Description

Modify Server Program.cs to support both HTTP and STDIO transports via a command-line option.

Implementation

Modify: src/CodingWithCalvin.MCPServer.Server/Program.cs

New Command Line Option

var transportOption = new Option<string>(
    name: "--transport",
    getDefaultValue: () => "http",
    description: "MCP transport: 'http' (HTTP/SSE server) or 'stdio' (STDIO transport)");

STDIO Mode Logic

if (transport == "stdio")
{
    // 1. Create RpcServer with well-known pipe name
    var rpcServer = new RpcServer(shutdownCts);
    await rpcServer.StartAsync(McpConstants.StdioPipeName);
    
    // 2. Wait for VS Extension to connect (with timeout)
    await rpcServer.WaitForConnectionAsync(TimeSpan.FromSeconds(60));
    
    // 3. Build MCP server with STDIO transport
    // Use Host.CreateDefaultBuilder() instead of WebApplication
    // Use WithStdioServerTransport() instead of WithHttpTransport()
    
    // 4. Run until shutdown
}
else // http mode - unchanged
{
    // Existing implementation
}

Error Handling

• Clear error message if VS doesn't connect within timeout
• Proper cleanup on CTRL+C / shutdown

Dependencies

• Requires RpcServer class (feat(shared): add McpConstants for STDIO pipe name #19 or similar)
• Requires McpConstants (feat(shared): add McpConstants for STDIO pipe name #19 or similar)

Acceptance Criteria

• --transport option added (http/stdio)
• HTTP mode unchanged (regression test)
• STDIO mode creates pipe server
• STDIO mode uses STDIO transport for MCP
• Timeout with helpful error message