fix: reduce Docker image size and free more CI disk space

Clean up Rust target/ and cargo registry after uv sync in the same RUN
command so build artifacts aren't committed to the layer (~1-2 GB saved).
Also remove more unused toolchains from the CI runner.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

.github/workflows/e2e.yml

@@ -14,7 +14,9 @@ jobs:
     steps:
       - name: Free up disk space
         run: |
-          sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache
+          sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc \
+            /opt/hostedtoolcache /usr/local/share/boost /usr/share/swift \
+            /opt/microsoft /opt/az
           docker system prune -af
           df -h /
 

e2e/Dockerfile

@@ -39,8 +39,9 @@ COPY resources/ ./resources/
 # Copy built dashboard from stage 1
 COPY --from=dashboard /app/dashboard/build ./dashboard/build/
 
-# Install Python deps and build Rust bindings
-RUN uv sync
+# Install Python deps and build Rust bindings, then clean up build artifacts
+# to keep the layer small (Rust target/ and cargo registry can be 1-2 GB)
+RUN uv sync && rm -rf /app/rust/target /root/.cargo/registry /root/.cargo/git
 
 # Wrap g++ with -fpermissive to fix MLX CPU JIT compilation with GCC 14
 # (GCC 14 treats _Float128/_Float32/_Float64 as built-in types, conflicting with MLX-generated code)