Add standalone Go build alongside VSCode extension

Ports all five tools to a single 7.5 MB Windows exe with an embedded
WebView2 window, file-based config, single-instance focus, and clean
shutdown. Adds build.ps1 to build both targets from one command.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

standalone/.gitignore

@@ -0,0 +1,4 @@
+hpl-toolbox.exe
+config.json
+.hpltoolbox.lock
+debug.log