PowerShell-first onboarding (most devs are on VS Code/Windows), a
Windows variant for the VS Code check task, and a .gitattributes rule
keeping shell scripts LF so Windows checkouts do not corrupt them.
Clone-to-first-change onboarding, plus .vscode launch/tasks/extensions
so F5 debugs the backend and a task runs both dev servers. Fix the
README manual path to run the backend on 5001 (the frontend proxies
there; the default 5000 loaded nothing).
