fix(app): keep Snapora alive when all BrowserWindows close

[aryasadeghy]

Electron's default window-all-closed behavior quits the app — even on macOS — when the last BrowserWindow goes away. LSUIElement: true only applies to packaged builds, so in npm run dev (and likely in any code path that spawns Electron without the packaged Info.plist) the app would silently quit between captures.

Reproduction (before this fix):

1. Fresh npm run dev.
2. First action: take an area capture (Cmd+Shift+2).
3. Selection overlay creates BrowserWindows; user commits the rect; overlays close().
4. window-all-closed fires → default → app.quit() → exit code 0.
5. The pending screencapture promise dies with the process; main.log ends at "spawning screencapture" with no follow-up.

The window-mode flow happened to work because screencapture's UI is a separate process — Snapora itself never opened or closed a window, so the event never fired. Doing window-then-area also worked because the HUD window stays in the BrowserWindow registry (it hide()s, not close()s) and keeps the count positive.

Fix: subscribe to window-all-closed and refuse to quit on macOS. Snapora is a menu-bar app — the tray keeps it running. The packaged build's LSUIElement was already doing this for production users; this hooks it for the dev build (and as a belt-and-suspenders production guard).

Summary

Type

• feat — new feature
• fix — bug fix
• docs — documentation only
• refactor — code restructure, no behavior change
• perf — performance improvement
• test — adds or changes tests
• chore / ci / build — tooling

Screenshots / recording

Test plan

• npm run lint
• npm run typecheck
• npm test
• Manual smoke: launched the app, exercised the changed feature
• Manual smoke: nothing else regressed

Clean-room confirmation

• I confirm this contribution is not derived from decompiled or leaked commercial software (see CONTRIBUTING.md).

Linked issues

Closes #