fix: Alpine Rust toolchain compatibility

- Remove rustup dependency from Dockerfile (not available in Alpine)
- Update Rust environment setup to handle both rustup and system Rust
- Fix musl-gcc linker configuration for Alpine containers
- Support both GitHub Actions (rustup) and Alpine container (system) environments

Dockerfile

@@ -24,8 +24,8 @@ RUN apk add --no-cache \
     sed \
     coreutils
 
-# Add Rust musl target
-RUN rustup target add x86_64-unknown-linux-musl
+# Install musl-dev for Rust musl targeting (Alpine handles this differently than rustup)
+RUN apk add --no-cache musl-dev
 
 # Create non-root user for builds
 RUN adduser -D -s /bin/bash builder && \
@@ -34,9 +34,10 @@ RUN adduser -D -s /bin/bash builder && \
 # Set working directory
 WORKDIR /workspace
 
-# Set environment variables for static linking
-ENV RUSTFLAGS="-C target-feature=+crt-static"
-ENV CC_x86_64_unknown_linux_musl="musl-gcc"
+# Set environment variables for musl static linking with Alpine's Rust
+ENV RUSTFLAGS="-C target-feature=+crt-static -C linker=musl-gcc"
+ENV CC="musl-gcc"
+ENV TARGET_CC="musl-gcc"
 ENV CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER="musl-gcc"
 
 # Default to builder user