feat(renovate): add Gitea update automation

Run Renovate in Kubernetes to create reviewed image update PRs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

renovate/renovate-compose.yaml

@@ -0,0 +1,17 @@
+services:
+  renovate:
+    image: renovate/renovate:44.83.2
+    container_name: renovate
+    restart: "no"
+    env_file:
+      - .env
+    environment:
+      RENOVATE_PLATFORM: gitea
+      RENOVATE_ENDPOINT: ${RENOVATE_ENDPOINT:?set RENOVATE_ENDPOINT}
+      RENOVATE_TOKEN: ${RENOVATE_TOKEN:?set RENOVATE_TOKEN}
+      RENOVATE_REPOSITORIES: ${RENOVATE_REPOSITORIES:?set RENOVATE_REPOSITORIES}
+      RENOVATE_CONFIG_FILE: /opt/renovate/config.js
+      RENOVATE_BASE_DIR: /tmp/renovate
+      LOG_LEVEL: ${LOG_LEVEL:-info}
+    volumes:
+      - ./config.js:/opt/renovate/config.js:ro