fix: Quit & Reopen could silently quit without ever reopening

[Alfredoalv13]

Summary

• This app enforces `requestSingleInstanceLock()`: if a new process can't acquire it, it calls `app.quit()` immediately (see the check right after `requestSingleInstanceLock()` in `main.ts`).
• Verified directly this session that this is what was silently eating the "Quit & Reopen" relaunch (from fix: relaunch via open instead of app.relaunch() so TCC grants are seen #11/fix: relaunch button could silently quit without reopening #13): the new process spawned via `open` would sometimes start up while the old process still held the lock, see "another instance is already running," and immediately quit itself - leaving neither process running, no window, no error.
• fix: relaunch button could silently quit without reopening #13's fix (delaying `app.exit()` by 500ms) didn't actually address this - delaying exit only makes the old process hold the lock longer, which makes this race more likely to bite, not less.
• Fix: explicitly call `app.releaseSingleInstanceLock()` before spawning the replacement process, so the new process can always acquire the lock regardless of exact timing between the two processes.

Test plan

• `tsc --noEmit` clean
• `npm test` - 94/94 files, 819/819 tests passing
• Manual: click "Quit & Reopen" from the permission banner repeatedly (10+ times in a row) and confirm the app reliably reopens every single time, not just most of the time