fix(ci): separate cross-compilation target from toolchain install

dtolnay/rust-toolchain resolves Blacksmith runner hostnames as Rust
targets on ARM64 runners. Split target addition into explicit rustup
command for cross-compilation builds.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/build-native.yml

@@ -46,8 +46,10 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
-        with:
-          targets: ${{ matrix.target }}
+
+      - name: Add Rust cross-compilation target
+        if: matrix.cross
+        run: rustup target add ${{ matrix.target }}
 
       - name: Cache Rust build artifacts
         uses: Swatinem/rust-cache@v2