v2: tune playback for bursty upstream + clean overflow handling

- Player: match webplayer.online's proven mpegts.js live-sync config
  (deep 30-90s buffer, 45s target latency, 1.1x catch-up). The upstream
  delivers in bursts with multi-second gaps (measured up to ~6s); the
  deep buffer rides over them so 4K HEVC plays smoothly.
- Hub: on subscriber buffer overflow, cleanly disconnect the client so
  it reconnects and resyncs from a TS packet boundary instead of
  dropping bytes mid-stream (which corrupted alignment / sync_byte).
- Enlarge per-client buffer (256 -> 2048 chunks).
- Refresh real1.m3u from upstream.

backend/api/ts.go

@@ -32,6 +32,9 @@ func (a *App) HandleTS(w http.ResponseWriter, r *http.Request) {
 			return
 		case <-sub.Done():
 			return
+		case <-sub.Overflow():
+			// Client fell too far behind; close so it reconnects and resyncs.
+			return
 		case chunk, ok := <-sub.Chan():
 			if !ok {
 				return