Improve launch skill (#4332)

* Improve launch skill

* talk about restarting
* suggest screenshots along the way
* save user-data-dir in workspace (so that we can leverage worktrees)
* gitignore user data dir

Seems to work pretty well.

* Fix cross-platform kill command in launch skill

Match VS Code process by --user-data-dir path instead of
"Code - Insiders" name, which doesn't match on Linux where
the process is named code-insiders.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>