chore: update Homebrew formula to v2.4.0

Add automated formula update job to publish.yml — after PyPI publish,
the workflow downloads the tarball, computes SHA256, updates the
formula, and commits. No manual step needed for future releases.

Revert formula to v2.3.0 (current working version) so the workflow
handles the v2.4.0 update after PyPI publish completes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: NetDevAutomate

.github/workflows/publish.yml

@@ -82,3 +82,47 @@ jobs:
       - name: Publish to PyPI
         uses: pypa/gh-action-pypi-publish@release/v1
         # No API token needed -- uses OIDC
+
+  update-formula:
+    needs: publish
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: main
+
+      - name: Wait for PyPI availability
+        run: |
+          VERSION="${GITHUB_REF_NAME#v}"
+          URL="https://files.pythonhosted.org/packages/source/s/studyctl/studyctl-${VERSION}.tar.gz"
+          for i in $(seq 1 30); do
+            if curl -sfI "$URL" >/dev/null 2>&1; then
+              echo "PyPI tarball available after ${i}0s"
+              break
+            fi
+            echo "Waiting for PyPI... (attempt $i/30)"
+            sleep 10
+          done
+
+      - name: Update Homebrew formula
+        run: |
+          VERSION="${GITHUB_REF_NAME#v}"
+          URL="https://files.pythonhosted.org/packages/source/s/studyctl/studyctl-${VERSION}.tar.gz"
+          SHA=$(curl -sL "$URL" | sha256sum | cut -d' ' -f1)
+          echo "Version: $VERSION"
+          echo "SHA256:  $SHA"
+          sed -i "s|studyctl-.*\.tar\.gz|studyctl-${VERSION}.tar.gz|" Formula/studyctl.rb
+          sed -i "s|sha256 \".*\"|sha256 \"${SHA}\"|" Formula/studyctl.rb
+          grep -A1 'url ' Formula/studyctl.rb
+
+      - name: Commit and push formula
+        run: |
+          VERSION="${GITHUB_REF_NAME#v}"
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add Formula/studyctl.rb
+          git diff --cached --quiet && echo "No changes" && exit 0
+          git commit -m "chore: update Homebrew formula to v${VERSION} [skip ci]"
+          git push