fix(rms_vad): correct types and threshold order in flush idempotency test

Two issues in flush_is_idempotent_and_leaves_clean_state from
581a098:

1. silence_close_samples and max_chunk_samples were cast `as u64`
   but with_thresholds takes usize — wouldn't compile.
2. enter_threshold was 0.005 and exit_threshold 0.01, which
   violates the hysteresis invariant (enter must be >= exit) and
   panics in debug_assert at runtime. Swap to 0.01 / 0.005 so the
   test actually runs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/transcription/src/streaming/rms_vad.rs

@@ -700,11 +700,11 @@ mod tests {
         // silence emits nothing (i.e. no stale onset / silent_tail
         // bookkeeping leaks into the next feed).
         let mut c = RmsVadChunker::with_thresholds(
-            0.005,
             0.01,
+            0.005,
             DEFAULT_SPEECH_ONSET_FRAMES,
-            (FRAME_SAMPLES * 4) as u64,
+            FRAME_SAMPLES * 4,
-            (FRAME_SAMPLES * 50) as u64,
+            FRAME_SAMPLES * 50,
         );
 
         let speech = constant_signal(FRAME_SAMPLES * 6, 0.02);