fix(main): R9 — guard the yt-dlp update throttle against a backward clock

shouldAutoCheckYtdlp compared (now - lastCheck) >= interval; a backward system-
clock correction leaves lastCheck in the future so the difference is negative and
the daily check never comes due again. Treat a future lastCheck as skewed and run
the check. The renderer scheduled-item promoter is inherently fire-once (promotion
flips the item out of 'saved'), so it can't double-fire on a backward jump — a
forward jump firing early is documented and accepted as minor.

Unit-tested. typecheck + 263 tests + eslint + prettier green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/ytdlpPolicy.ts

@@ -21,5 +21,10 @@ export function shouldAutoCheckYtdlp(
 ): boolean {
   if (!enabled) return false
   if (!lastCheck) return true
+  // A backward system-clock correction can leave `lastCheck` in the "future"
+  // relative to `now`, making `now - lastCheck` negative so the daily check would
+  // never come due again. Treat a future timestamp as skewed/bogus and run the
+  // check rather than waiting out a negative interval (R9).
+  if (lastCheck > now) return true
   return now - lastCheck >= intervalMs
 }