refactor: simplify Docker build by removing cross-compilation and using native build only

Author: csjones

Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1
 
 # Base image and static SDK have to be updated together.
-FROM --platform=$BUILDPLATFORM swift:6.1 AS builder
+FROM swift:6.1 AS builder
 WORKDIR /workspace
 
 # Install Swift static SDK for better portability
@@ -12,21 +12,9 @@ RUN swift sdk install \
 # Copy source files
 COPY . /workspace
 
-# Build with static SDK and cross-compilation support
-ARG TARGETPLATFORM
-RUN --mount=type=cache,target=/workspace/.build,id=build-$TARGETPLATFORM \
-    echo "Building for platform: $TARGETPLATFORM" && \
-    swift sdk list && \
-    case "$TARGETPLATFORM" in \
-      "linux/amd64") \
-        swift build -c release --swift-sdk swift-6.1-RELEASE_static-linux-0.0.1 && \
-        cp /workspace/.build/*/release/subtree /workspace/subtree ;; \
-      "linux/arm64") \
-        swift build -c release --swift-sdk swift-6.1-RELEASE_static-linux-0.0.1 && \
-        cp /workspace/.build/*/release/subtree /workspace/subtree ;; \
-      *) \
-        echo "Unsupported platform: $TARGETPLATFORM" && exit 1 ;; \
-    esac
+# Build with static SDK using native compilation
+RUN swift build -c release --swift-sdk swift-6.1-RELEASE_static-linux-0.0.1 && \
+    find /workspace/.build -name "subtree" -type f -executable -exec cp {} /workspace/subtree \;
 
 # Final minimal runtime image
 FROM scratch AS runner