perf: faster stream startup

- Stop sending no-store on vendored player libraries: hls.min.js and
  mpegts.min.js (~750 KB) were re-downloaded on every player open
- hls.js: start with 1 live segment instead of 3, lower buffer-first
  threshold 1.5s -> 0.8s, poll buffer every 100ms
- mpegts.js: initial stash 512KB -> 128KB, start at 0.5s buffered
- Live FFmpeg: -hls_init_time 1 closes the first segment after ~1s

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

bin/api/streaming_handler.dart

@@ -220,8 +220,11 @@ Handler createLiveStreamHandler(
         ..._liveVideoArgs(quality, useNvidiaGpu),
         ..._audioArgs(withFilters: false),
         // HLS sliding window: 10 x 2s segments (lower live latency than the
-        // previous 20-segment window while still safe for iOS)
+        // previous 20-segment window while still safe for iOS).
+        // hls_init_time 1: first segment closes after ~1s so playback can
+        // start sooner; subsequent segments use hls_time.
         '-f', 'hls',
+        '-hls_init_time', '1',
         '-hls_time', '2',
         '-hls_list_size', '10',
         '-hls_flags', 'delete_segments+independent_segments',