Fix CI: symlink python-zig to zig for cargo-zigbuild

The ziglang pip package installs as python-zig, not zig.
cargo-zigbuild needs zig in PATH, so create a symlink.

https://claude.ai/code/session_01EcsZDNeWn56wFqryb4Wq7r

.github/workflows/ci.yml

@@ -48,6 +48,9 @@ jobs:
     - name: Install zig and cargo-zigbuild
       run: |
         pip install --break-system-packages ziglang
+        # ziglang pip package installs as python-zig, symlink to zig for cargo-zigbuild
+        sudo ln -sf "$(which python-zig)" /usr/local/bin/zig
+        zig version
         command -v cargo-zigbuild || cargo install cargo-zigbuild
 
     - run: make check-fmt