fix(ci): move x86_64 macOS wheel build to macos-15-intel (#146)

macos-13 runners were retired by GitHub, so the x86_64-apple-darwin
build job queued forever and the publish never ran.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/publish-pypi.yml

@@ -89,7 +89,9 @@ jobs:
             target: x86_64-unknown-linux-gnu
           - os: ubuntu-latest
             target: aarch64-unknown-linux-gnu
-          - os: macos-13
+          # macos-13 was retired by GitHub; macos-15-intel is the remaining
+          # Intel runner label (available through 2027).
+          - os: macos-15-intel
             target: x86_64-apple-darwin
           - os: macos-14
             target: aarch64-apple-darwin