ci: add tag-based release pipeline with coverage and source archive

.drone.yml

@@ -2,6 +2,11 @@ kind: pipeline
 type: docker
 name: go-lib/util
 
+trigger:
+  event: tag
+  ref:
+    - refs/tags/v*
+
 steps:
 - name: test
   image: golang:1.25.8
@@ -14,3 +19,23 @@ steps:
     - bash scripts/check-coverage.sh .build/coverage.out 80
     - go install golang.org/x/vuln/cmd/govulncheck@latest
     - govulncheck -json ./... > vulncheck.json
+
+- name: package
+  image: golang:1.25.8
+  commands:
+    - tar czf .build/sources.tar.gz --exclude=.build --exclude=.git --exclude=.drone.yml .
+  when:
+    status: success
+
+- name: release
+  image: plugins/gitea-release
+  settings:
+    api_key:
+      from_secret: gitea_token
+    files: 
+      - .build/coverage.txt
+      - .build/sources.tar.gz
+    title: ${DRONE_TAG}
+    note: "Release ${DRONE_TAG}\n\nCoverage report: coverage.txt"
+  when:
+    status: success