ci: keep gitea workflows only, harden and speed up pipelines

Drop duplicated .github/workflows (helm blocks ported to .gitea deploy first). Add ci concurrency with cancel on branches, pin checkout to SHA and prettier to 3.9.8, registry layer cache for image builds. renovate-run gains config validation and dry-run input.

.gitea/workflows/renovate-ci.yaml

@@ -12,7 +12,7 @@ jobs:
     runs-on: [self-hosted, linux, arch, homelab]
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Validate Renovate Compose draft
         shell: bash