Add merged branch release notes to Gitea release body (#4)

Generates release notes from merged branches since last tag and
includes them in the release body via Gitea API.

Reviewed-on: #4

.woodpecker/release.yaml

@@ -15,16 +15,23 @@ steps:
     depends_on: [test]
 
   - name: release
-    image: alpine/curl
+    image: git.unkin.net/unkin/almalinux9-base:20260325
     environment:
       DRONECI_PASSWORD:
         from_secret: DRONECI_PASSWORD
     commands:
       - |
+        PREV_TAG=$(git describe --tags --abbrev=0 HEAD^ 2>/dev/null || echo "")
+        if [ -n "$PREV_TAG" ]; then
+          NOTES=$(git log "${PREV_TAG}..${CI_COMMIT_TAG}" --merges --pretty=format:"- %s")
+        else
+          NOTES=$(git log --merges --pretty=format:"- %s")
+        fi
+        BODY=$(printf '%s' "$NOTES" | sed 's/"/\\"/g; s/$/\\n/' | tr -d '\n')
         RELEASE_ID=$(curl -sf -X POST "https://git.unkin.net/api/v1/repos/${CI_REPO}/releases" \
           -u "droneci:$DRONECI_PASSWORD" \
           -H "Content-Type: application/json" \
-          -d "{\"tag_name\":\"${CI_COMMIT_TAG}\",\"name\":\"${CI_COMMIT_TAG}\"}" \
+          -d "{\"tag_name\":\"${CI_COMMIT_TAG}\",\"name\":\"${CI_COMMIT_TAG}\",\"body\":\"${BODY}\"}" \
           | grep -o '"id":[0-9]*' | head -1 | cut -d: -f2)
         curl -sf -X POST "https://git.unkin.net/api/v1/repos/${CI_REPO}/releases/${RELEASE_ID}/assets" \
           -u "droneci:$DRONECI_PASSWORD" \