v2: mpegts.js + single-upstream fan-out hub (no FFmpeg/HLS)

Replaces the FFmpeg -> MediaMTX -> HLS pipeline with a raw MPEG-TS
fan-out architecture:

- Go stream.Hub holds ONE upstream connection per active channel and
  broadcasts the raw TS bytes to all connected browsers via /ts.
  The IPTV provider only ever sees one IP (the server), no matter how
  many viewers are watching (shared single-channel model).
- Frontend uses mpegts.js to play the raw TS in-browser via MSE,
  fixing HEVC/H.265 4K streams that HLS could not package.
- Dropped FFmpeg, MediaMTX, RTMP/RTSP, HLS proxy, playback/ingest
  modes, the OBS source toggle, and FFmpeg health stats.
- UI look preserved (fullscreen video, collapsible sidebar, status
  bar, upstream-down banner, hourly playlist auto-refresh).

Tradeoff: loses iOS Safari (no MSE/mpegts.js); fixes desktop/Android
playback of both H.264 and H.265.

backend/api/status.go

@@ -20,29 +20,22 @@ func (a *App) HandleStatus(w http.ResponseWriter, r *http.Request) {
 	status := a.Status
 	a.mu.RUnlock()
 
-	// Attach live stream health metrics when FFmpeg is running
-	status.Health = a.FFmpeg.Health()
-
-	// Auto-clear transitioning once FFmpeg is producing health data.
-	// If no progress arrives for a while after a channel switch, flag upstream_down
-	// so all watchers see an "Upstream down?" warning via polling.
-	if status.Transitioning && status.Health != nil && status.Health.Speed != "" {
+	// Detect upstream health from the hub. Once the hub receives data, the
+	// channel is considered live; if no data arrives within the threshold
+	// after a switch, flag upstream_down so all watchers see the warning.
+	gotData, since := a.Hub.GotData()
+	if status.Transitioning && gotData {
 		a.mu.Lock()
 		a.Status.Transitioning = false
 		a.Status.UpstreamDown = false
 		a.mu.Unlock()
 		status.Transitioning = false
 		status.UpstreamDown = false
-	} else if status.Transitioning {
-		a.mu.RLock()
-		switchStartedAt := a.SwitchStartedAt
-		a.mu.RUnlock()
-		if !switchStartedAt.IsZero() && time.Since(switchStartedAt) >= upstreamDownAfter {
-			a.mu.Lock()
-			a.Status.UpstreamDown = true
-			a.mu.Unlock()
-			status.UpstreamDown = true
-		}
+	} else if status.Transitioning && !gotData && since >= upstreamDownAfter {
+		a.mu.Lock()
+		a.Status.UpstreamDown = true
+		a.mu.Unlock()
+		status.UpstreamDown = true
 	}
 
 	w.Header().Set("Content-Type", "application/json")