Fix Critical: streaming race, dirty buffer, dropped tail, fragmented header

- SeekBeyondBuffer and LoadTrackStreaming assign _activeStreamingTask before
  awaiting; DrainActiveStreamingTaskAsync awaits previous task before new
  stream starts, closing the concurrent-seek race on the JS StreamDecoder
- Always slice ArrayPool buffer to currentBytes before sending to JS interop;
  eliminates stale bytes from prior rentals reaching the audio decoder
- getSampleAlignedChunkSize accepts streamComplete flag; bypasses minimum
  chunk guard on final tail so trailing bytes are decoded, not dropped
- StreamDecoder accumulates headerSearchChunks until parseHeader succeeds,
  with 256 KB MAX_HEADER_SEARCH_BYTES bound; handles fragmented first chunks
  and extended WAV headers with LIST/INFO/JUNK chunks
- markStreamComplete early-returns when streamComplete already set to prevent
  double-drain and incorrect streamingCompleted flag after partial failure
- processedBytes advances only after successful decode; failed segments leave
  cursor in place rather than permanently skipping audio
- AudioInteropService.MarkStreamCompleteAsync wires C# loop exit to JS decoder
  ensuring tail drain fires even when Content-Length header is absent

DeepDrftWeb/Interop/audio/index.ts

@@ -45,6 +45,12 @@ const DeepDrftAudio = {
         return player.startStreamingPlayback();
     },
 
+    markStreamComplete: async (playerId: string): Promise<StreamingResult> => {
+        const player = audioPlayers.get(playerId);
+        if (!player) return { success: false, error: 'Player not found' };
+        return player.markStreamComplete();
+    },
+
     ensureAudioContextReady: async (playerId: string): Promise<AudioResult> => {
         const player = audioPlayers.get(playerId);
         if (!player) return { success: false, error: 'Player not found' };