Reduce BROADCAST_CAPACITY to maintain metadata synchronization

Changed from 4096 to 128 messages (~10s buffer instead of ~5min).

The large buffer was causing metadata drift: clients could be hearing
audio 5 minutes behind the metadata endpoint and ICY metadata updates.

With TimerNode pacing the stream to real-time, we only need a small
buffer for network jitter. This keeps metadata properly synchronized
with the actual audio being played.

pmoaudio-ext/src/sinks/streaming_flac_sink.rs

@@ -81,9 +81,10 @@ use tracing::{debug, error, info, trace, warn};
 const DEFAULT_ICY_METAINT: usize = 16000;
 
 /// Broadcast channel capacity for FLAC bytes.
-/// Increased to 4096 to handle network backpressure and late-joining clients.
-/// At ~12-15 chunks/sec (8KB each), this provides ~5 minutes of buffer.
-const BROADCAST_CAPACITY: usize = 4096;
+/// Set to 128 to provide ~10 seconds of buffer for network jitter.
+/// With TimerNode pacing the stream to real-time, this is sufficient
+/// while keeping metadata synchronized (larger buffers cause metadata drift).
+const BROADCAST_CAPACITY: usize = 128;
 
 /// Snapshot of track metadata at a point in time.
 ///