fix(release): guard PREV_TAG with rev-parse before using in log range

If PREV_TAG is a malformed or non-reachable tag name, git log fails
with exit 128 under set -e. Validate with git rev-parse --verify first
and fall back to a full log if it doesn't resolve.

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

.gitea/workflows/release.yml

@@ -64,7 +64,7 @@ jobs:
           API="${GITHUB_API_URL}/repos/${GITHUB_REPOSITORY}/releases"
 
           PREV_TAG=$(git tag --sort=-version:refname | { grep -v "^${TAG}$" || true; } | head -1)
-          if [ -n "$PREV_TAG" ]; then
+          if [ -n "$PREV_TAG" ] && git rev-parse --verify "${PREV_TAG}" >/dev/null 2>&1; then
             NOTES=$(git log "${PREV_TAG}..${TAG}" --pretty=format:"- %s" --no-merges)
           else
             NOTES=$(git log --pretty=format:"- %s" --no-merges)