apps/vscode 'Run Extension' pre-launch task calls a nonexistent watch script

[nealrichardson]

Bug

The Run Extension launch config in apps/vscode/.vscode/launch.json uses "preLaunchTask": "${defaultBuildTask}". The default build task in apps/vscode/.vscode/tasks.json is:

{ "type": "npm", "script": "watch", "problemMatcher": "$tsc-watch", "isBackground": true, ... }

apps/vscode/package.json has no watch script (it has build, dev, build-test, ...), so F5 from the apps/vscode folder fails at the pre-launch step. The root .vscode/tasks.json has the same npm: watch task, although the root "Run VS Code Extension" config doesn't use it.

Also, $tsc-watch is the wrong problem matcher even if a watch script existed, because the build is esbuild (tsx build.ts), not tsc --watch.

Fix options

1. Point the default build task at an existing script (e.g. yarn dev, which is tsx build.ts dev), make it non-background, and use problemMatcher: [] or an esbuild matcher. That also needs the other workspaces to be built, so it may have to be turbo run build --filter quarto... from the repo root, like vscode:prepublish does.
2. Or add a real watch script. Note that the turbo 2 upgrade plan (deps-upgrade-turbo.md) also drops a broken root watch script, so coordinate with that.

Also update the root .vscode/tasks.json for consistency, and check that apps/vscode/CONTRIBUTING.md describes the debug flow correctly.

Found during the dependency-upgrade research.