librespot: add native-tls feature (required by librespot-oauth)

oauth2 crate gates TLS backends behind features; without native-tls,
librespot-oauth fails to compile with compile_error!. The default
features include native-tls, but we use --no-default-features for
minimal build.

infra/librespot/Dockerfile

@@ -19,7 +19,7 @@ WORKDIR /src
 # Lower = less memory pressure, slower build. Higher = OOM risk.
 RUN cargo build --release --jobs 2 \
     --no-default-features \
-    --features="pulseaudio-backend"
+    --features="pulseaudio-backend,native-tls"
 
 FROM debian:bookworm-slim