chore(deps): remove unused rubato dependency

rubato was listed in Cargo.toml but never imported anywhere in src/.
WASAPI's AUTOCONVERTPCM handles all our resampling needs. Dropping it
shrinks the dep graph and closes the Dependabot 0.16 -> 2.0 PR noise.

Author: Yakov Tchenak

Cargo.lock

@@ -29,9 +29,6 @@ winit = "0.30"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 
-# Audio resampling — converts between sample rates
-rubato = "0.16"
-
 # Structured logging — modern replacement for println! debugging
 tracing = "0.1"
 tracing-subscriber = "0.3"