feat: add [skip ci] support and tag trigger

- Skip CI when commit message contains [skip ci]
- Add tag trigger: push 'submit' or 'submit-*' tag to grade
- Prevents unnecessary CI runs during initialization

.gitea/workflows/autograde.yml

@@ -4,14 +4,39 @@ on:
   push:
     branches:
       - main
-  workflow_dispatch:
+    tags:
+      - 'submit'        # 学生打 submit 标签触发评分
+      - 'submit-*'      # 或 submit-v1, submit-final 等
+  workflow_dispatch:    # 手动触发
 
 permissions:
   contents: read
   pull-requests: write
 
 jobs:
+  # 检查是否应该跳过 CI
+  check-skip:
+    runs-on: docker
+    container:
+      image: alpine:latest
+    outputs:
+      should_skip: ${{ steps.check.outputs.skip }}
+    steps:
+      - name: Check for skip CI
+        id: check
+        run: |
+          COMMIT_MSG="${{ github.event.head_commit.message }}"
+          # 检查是否包含 [skip ci], [ci skip], [no ci] 等
+          if echo "$COMMIT_MSG" | grep -qiE '\[(skip ci|ci skip|no ci|skip actions)\]'; then
+            echo "skip=true" >> $GITHUB_OUTPUT
+            echo "⏭️ Skipping CI due to commit message: $COMMIT_MSG"
+          else
+            echo "skip=false" >> $GITHUB_OUTPUT
+          fi
+
   grade:
+    needs: check-skip
+    if: needs.check-skip.outputs.should_skip != 'true'
     runs-on: docker
     container:
       image: gradle:9.0-jdk21