fix: vec allocation for desktop AudioRing (match Android fix)

Same fix as Android: Box::new([0i16; 16384]) allocates 32KB on the
stack before moving to heap. Use vec![].into_boxed_slice() for
direct heap allocation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-client/src/audio_ring.rs

@@ -18,7 +18,7 @@ const RING_MASK: usize = RING_CAPACITY - 1;
 
 /// Lock-free single-producer single-consumer ring buffer for i16 PCM samples.
 pub struct AudioRing {
-    buf: Box<[i16; RING_CAPACITY]>,
+    buf: Box<[i16]>,
     /// Monotonically increasing write cursor. ONLY written by producer.
     write_pos: AtomicUsize,
     /// Monotonically increasing read cursor. ONLY written by consumer.
@@ -40,7 +40,7 @@ impl AudioRing {
     pub fn new() -> Self {
         debug_assert!(RING_CAPACITY.is_power_of_two());
         Self {
-            buf: Box::new([0i16; RING_CAPACITY]),
+            buf: vec![0i16; RING_CAPACITY].into_boxed_slice(),
             write_pos: AtomicUsize::new(0),
             read_pos: AtomicUsize::new(0),
             overflow_count: AtomicU64::new(0),