style(host/pad-audio): drop a redundant f32 cast in the tone devtest

clippy's `unnecessary_cast` fires on it, which fails CI's -D warnings.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/audio/windows/pad_endpoint.rs

@@ -1615,7 +1615,7 @@ pub(crate) fn render_test_tone(endpoint_id: &str, seconds: u32, hz: f32) -> Resu
             continue;
         }
         for f in 0..n {
-            let s = (phase.sin() * 0.5) as f32;
+            let s = phase.sin() * 0.5;
             phase += step;
             if phase >= std::f32::consts::TAU {
                 phase -= std::f32::consts::TAU;