Simplify the quit-with-running-sites dialog and add a settings home for it

[shaunandrews]

Related issues

How AI was used in this PR

Designed collaboratively in a Claude Code session (dialog copy and interaction explored against several alternatives), then implemented and ported to trunk by Claude. All changes reviewed by @shaunandrews.

Proposed Changes

The first time a new user quits Studio with a running site, they hit a native dialog that asks them to configure a three-way policy ("Keep running" / "Auto-start" / "Stop") explained by a bullet-list legend in the body text — a heavy, confusing decision at the exact moment they've decided to leave. And its "Don't ask again" checkbox wrote a preference that no UI exposed, so one click made the choice permanent.

This PR reframes the dialog as a single question the buttons can answer directly:

"Keep your sites running?" — Keep running (default) or Stop sites, with the running sites' names in the message so the stakes are concrete (falling back to a count when names are long or there are more than two).

• Stopping now means auto-start later. The dialog's "Stop sites" maps to stop-and-restart-on-next-launch, which is what most people quitting an app expect. The hard "stop and stay stopped" option lives in Settings for those who want it.
• "Don't ask again" became "Remember my choice", and the preference now has a home: a "When quitting with running sites" setting (Ask every time / Keep sites running / Stop, restart on next launch / Stop sites) in both the legacy renderer's Preferences tab and the agentic UI's Settings. Choosing "Ask every time" brings the dialog back — the checkbox is no longer a one-way door.
• A dev-only menu item (Studio menu → "Show Quit Dialog (dev only)") previews the dialog without quitting or persisting anything, using real running-site names or sample names when nothing is running.

No migration needed: the stored preference and its semantics are unchanged; existing saved choices (including auto-start) are honored as before.

Testing Instructions

1. Run a dev build, open the Studio app menu → Show Quit Dialog (dev only) to preview the dialog (works with or without running sites; choice is logged, not applied).
2. With a site running and no saved preference, quit Studio — the new dialog appears. Keep running leaves the site served after quit; Stop sites stops it and the site starts again on next launch.
3. Check Remember my choice with either button, relaunch, and confirm Settings shows the saved value — legacy UI: Settings → Preferences; agentic UI (ENABLE_AGENTIC_UI=true): Settings.
4. Set the setting back to Ask every time and confirm the dialog returns on quit.
5. Set it to Stop sites and confirm quitting stops sites without a dialog and they stay stopped on relaunch.

⚠️ Visual change: needs human review in light + dark mode (settings selects in both UIs).

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

🤖 Generated with Claude Code

[fredrikekelund]

@shaunandrews, I didn't realize you had a PR for this (I didn't see anything in STU-1908). I put out #4140 this morning. Given that this PR is still in draft, I will go ahead and close it in favor of the other PR. Let me know if I'm missing anything