fix(client-core): pad-audio references the WASAPI module by its mounted name

The Windows build of pf-client-core has been red on main since the
pad-audio merge (#23): pad_audio.rs calls
`crate::audio_wasapi::device_by_id`, but lib.rs mounts audio_wasapi.rs AS
`crate::audio` via the #[path] per-OS swap — the `audio_wasapi` module
name never exists. Windows-gated call site, so every Linux leg stayed
green while both `windows / build` targets failed E0433.

One-line rename to the mounted path (+ the comment that pointed readers
at the phantom name). Verification is the PR's own windows leg — the
crate builds on no other platform this path compiles on.

crates/pf-client-core/src/pad_audio.rs

@@ -921,9 +921,9 @@ fn pad_render_thread(
         const BLOCK_ALIGN: usize = PAD_CHANNELS * 4; // f32 interleaved
         let enumerator = wasapi::DeviceEnumerator::new().context("DeviceEnumerator")?;
         // Not `get_device`: that helper resolves through a freed string — see
-        // [`crate::audio_wasapi::device_by_id`].
+        // [`crate::audio::device_by_id`] (audio_wasapi.rs, mounted as `crate::audio` on
-        let device =
+        // Windows by lib.rs's `#[path]` swap — there is no `audio_wasapi` module name).
-            crate::audio_wasapi::device_by_id(&enumerator, &Direction::Render, endpoint_id)
+        let device = crate::audio::device_by_id(&enumerator, &Direction::Render, endpoint_id)
             .map_err(|e| anyhow!("correlated endpoint not found: {e:#}"))?;
         let mut audio_client = device.get_iaudioclient().context("IAudioClient")?;
         // FL|FR|BL|BR: front pair = the pad's speaker, back pair = the voice coils.