fix(mcp): add EUPL-1.2 header and fix empty struct schema

- Add missing SPDX license header to mcp.go
- Return empty schema object for zero-field structs instead of nil

Co-Authored-By: Virgil <virgil@lethean.io>

mcp/mcp.go

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: EUPL-1.2
+
 // Package mcp provides a lightweight MCP (Model Context Protocol) server for CLI use.
 // For full GUI integration (display, webview, process management), see core-gui/pkg/mcp.
 package mcp

mcp/registry.go

@@ -44,7 +44,7 @@ func structSchema(v any) map[string]any {
 		return nil
 	}
 	if t.NumField() == 0 {
-		return nil
+		return map[string]any{"type": "object", "properties": map[string]any{}}
 	}
 
 	properties := make(map[string]any)