fix(bridge): WAV header data_size for IEEE float32 (was 16-bit byte count)

- finishWav call sites accumulated n*4 (stereo 16-bit) but float32 writer
  emits n*8 bytes -> RIFF/data chunk sizes half the real value; players and
  soundfile truncated renders to half length
- gate test now asserts file size == 44 + data_size to catch this

tests/test_lossless_compliance.py

@@ -43,6 +43,8 @@ def wav_format_info(path):
     with open(path, "rb") as f:
         b = f.read(44)
     assert b[:4] == b"RIFF" and b[8:12] == b"WAVE", "not RIFF/WAVE"
+    data_size = struct.unpack_from("<I", b, 40)[0]
+    assert os.path.getsize(path) == 44 + data_size, "data chunk size mismatch"
     return {
         "fmt_tag": struct.unpack_from("<H", b, 20)[0],
         "channels": struct.unpack_from("<H", b, 22)[0],