Reels: record for Instagram from the phone

Timed recording (15/30/60/90s, auto-stop in the output) with 9:16
1080x1920 as the default format; countdown on the record button. New
/api/recordings (list) + /recordings static + delete endpoint; the Out tab
lists recorded reels with a download link (save to the phone, share to
Instagram) and delete. recStop returns name/url and recSaved carries them
so a just-recorded reel is one tap away. Transcode lightened for the Pi
(ultrafast, 3 threads, nice -10): no hardware H.264 encoder on the Pi 5,
and a full-core encode can brown the box out.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/css/mobile.css

@@ -142,3 +142,5 @@ textarea { width: 100%; min-height: 90px; resize: vertical; }
 }
 #tabs button small { font-size: 9px; }
 #tabs button.active { opacity: 1; color: var(--accent); }
+.item a.dl { flex: 0 0 auto; padding: 7px 12px; border: 1px solid var(--line); border-radius: 9px; background: rgba(76,175,80,.15); border-color: #4caf50; text-decoration: none; color: #d9ffd9; }
+#rec-status a { color: #8cf5a0; }