ci: publish a GitHub Release automatically on version tags

.github/workflows/release.yml

@@ -0,0 +1,48 @@
+name: Release
+
+on:
+  push:
+    tags: ['v*']
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    name: Publish GitHub Release
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Extract release notes from CHANGELOG
+        run: |
+          version="${GITHUB_REF_NAME#v}"
+          awk -v v="$version" '
+            $0 == "## [" v "]" || index($0, "## [" v "] ") == 1 { found = 1; next }
+            found && /^## \[/ { exit }
+            found && /^\[[^]]+\]: / { exit }
+            found { print }
+          ' CHANGELOG.md > release-notes.md
+
+          if [ ! -s release-notes.md ]; then
+            echo "::error::CHANGELOG.md has no section for [$version]. Add it before tagging."
+            exit 1
+          fi
+
+      - name: Publish release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          prerelease=""
+          case "$GITHUB_REF_NAME" in
+            *-*) prerelease="--prerelease" ;;
+            *)   prerelease="--latest" ;;
+          esac
+
+          gh release create "$GITHUB_REF_NAME" \
+            --verify-tag \
+            --title "rhttp $GITHUB_REF_NAME" \
+            --notes-file release-notes.md \
+            $prerelease