feat(ci): add GitOps pipeline with Gitea Actions and ArgoCD

- Add Gitea Actions workflow for building and pushing Docker images
- Configure ArgoCD Application for auto-sync deployment
- Update Helm values to use Gitea container registry
- Add setup documentation for GitOps configuration

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yaml

@@ -0,0 +1,63 @@
+name: Build and Push
+
+on:
+  push:
+    branches:
+      - master
+      - main
+  pull_request:
+    branches:
+      - master
+      - main
+
+env:
+  REGISTRY: git.kube2.tricnet.de
+  IMAGE_NAME: tho/taskplaner
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ secrets.REGISTRY_USERNAME }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=sha,prefix=
+            type=ref,event=branch
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/master' }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache
+          cache-to: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache,mode=max
+
+      - name: Update Helm values with new image tag
+        if: github.event_name != 'pull_request'
+        run: |
+          SHORT_SHA=$(echo "${{ github.sha }}" | cut -c1-7)
+          sed -i "s/^  tag:.*/  tag: \"${SHORT_SHA}\"/" helm/taskplaner/values.yaml
+          git config user.name "Gitea Actions"
+          git config user.email "actions@git.kube2.tricnet.de"
+          git add helm/taskplaner/values.yaml
+          git commit -m "chore: update image tag to ${SHORT_SHA} [skip ci]" || echo "No changes to commit"
+          git push || echo "Push failed - may need to configure git credentials"