fix(Dockerfile): install Rust via rustup for node-crc compatibility

infra/docker/Dockerfile.discord-gateway

@@ -12,9 +12,13 @@ RUN groupadd --system app && useradd --system -g app app
 # and ffmpeg for voice transmit (PCM to OggOpus encoding)
 # This is done early to cache this expensive layer
 RUN apt-get update -qq && apt-get install -y -qq --no-install-recommends \
-    python3 make g++ rustc cargo ffmpeg \
+    python3 make g++ ffmpeg curl ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
+# Install Rust via rustup (Debian's rustc/cargo is too old for node-crc)
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain stable
+ENV PATH="/root/.cargo/bin:${PATH}"
+
 # Use bundled node headers for native addon compilation
 ENV npm_config_nodedir=/usr/local