fix(daemon): defer probeCancel so a panic mid-diagnostic still releases ctx

DetectHWAccelDiagnostic spawns subprocess calls; an unexpected panic
(broken ffmpeg binary, OOM mid-exec) would otherwise leave the
WithTimeout context dangling until natural expiry. defer keeps the
goroutine + timer reachable until runDaemonStart returns, but on a
long-lived daemon that's the process lifetime anyway — same effective
cost, with the safety guarantee.

internal/cmd/daemon.go

@@ -152,8 +152,8 @@ func runDaemonStart() error {
 	// startup forever.
 	ffmpegResolved, _ := mediainfo.ResolveFFmpeg(cfg.Library.FFmpegPath)
 	probeCtx, probeCancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer probeCancel() // guard against a panic inside DetectHWAccelDiagnostic
 	hwDiag := engine.DetectHWAccelDiagnostic(probeCtx, ffmpegResolved)
-	probeCancel()
 	log.Println(hwDiag.LogLine())
 	hwAccelPick := hwDiag.Pick
 	maxTranscodeHeight := 1080