Add release workflow: auto-create a GitHub Release on version bump

On every push to main, compares extension.json's version field against
the previous commit's. If it changed, tags and creates a GitHub Release
(vX.Y.Z, with auto-generated notes from merged PRs) for that version —
automating what has so far been done by hand after each version bump
(matches the existing v0.9.0/v0.10.0/v0.11.0 releases: same tag naming,
same --generate-notes-style body).

Guards against re-creating a release that already exists (idempotent on
workflow re-runs or a version merged more than once).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: jmnote

.github/workflows/release.yml

@@ -0,0 +1,41 @@
+name: release
+
+on:
+  push:
+    branches: [main]
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
+
+      - name: Check whether extension.json's version changed
+        id: version
+        run: |
+          current=$(jq -r .version extension.json)
+          previous=$(git show HEAD^:extension.json 2>/dev/null | jq -r .version 2>/dev/null || echo "")
+          echo "current=$current" >> "$GITHUB_OUTPUT"
+          if [ "$current" != "$previous" ]; then
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Create GitHub release
+        if: steps.version.outputs.changed == 'true'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          TAG: v${{ steps.version.outputs.current }}
+        run: |
+          if gh release view "$TAG" >/dev/null 2>&1; then
+            echo "Release $TAG already exists, skipping."
+            exit 0
+          fi
+          gh release create "$TAG" --title "$TAG" --generate-notes