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>

helm/taskplaner/values.yaml

@@ -3,12 +3,13 @@
 replicaCount: 1
 
 image:
-  repository: taskplaner
-  pullPolicy: IfNotPresent
+  repository: git.kube2.tricnet.de/tho/taskplaner
+  pullPolicy: Always
   # Overrides the image tag whose default is the chart appVersion
-  tag: ""
+  tag: "latest"
 
-imagePullSecrets: []
+imagePullSecrets:
+  - name: gitea-registry-secret
 nameOverride: ""
 fullnameOverride: ""