ci: add automatic semver tagging on merge to main

.gitea/workflows/docker-build.yaml

@@ -14,6 +14,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+        with:
+          fetch-depth: 0
 
       - name: Clone HKUDS/nanobot source
         run: git clone --depth 1 https://github.com/HKUDS/nanobot.git external-nanobot
@@ -40,7 +42,7 @@ jobs:
             type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
 
       - name: Build and push
-        uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf # v7
+        uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf # v7.2.0
         with:
           context: external-nanobot
           file: external-nanobot/Dockerfile
@@ -48,3 +50,13 @@ jobs:
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           pull: true
+
+      - name: Bump version and push tag
+        if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+        uses: anothrNick/github-tag-action@4ed44965e0db8dab2b466a16da04aec3cc312fd8 # v1.75.0
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          DEFAULT_BUMP: patch
+          RELEASE_BRANCHES: main
+          WITH_V: true
+          GIT_API_TAGGING: false