Complete JSON marshal pattern refactoring

All changes complete and tested:
- Created marshalToResponse helper function
- Added comprehensive unit tests (8 test cases, all passing)
- Updated all 6 MCP methods (listTools, callTool, listResources, readResource, listPrompts, getPrompt)
- Reduced code from 1011 to 972 lines (39 lines removed)
- All MCP package tests pass
- Build successful, code formatted and linted

Note: Pre-existing launcher test failures are unrelated to this refactoring

Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Author: Claude

main.go

@@ -13,7 +13,7 @@ var log = logger.New("main:main")
 
 func main() {
 	log.Print("Starting MCP Gateway application")
-	
+
 	// Build version string with metadata
 	versionStr := buildVersionString()
 	log.Printf("Built version string: %s", versionStr)