Add development setup guide and shared VS Code config

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).

.gitignore

@@ -28,7 +28,11 @@ env/
 
 # IDE
 .idea/
-.vscode/
+.vscode/*
+# Share the team's launch/tasks/extensions; keep personal settings out.
+!.vscode/launch.json
+!.vscode/tasks.json
+!.vscode/extensions.json
 *.swp
 *.swo
 *~