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/config.js

@@ -0,0 +1,41 @@
+module.exports = {
+  platform: 'gitea',
+  endpoint: process.env.RENOVATE_ENDPOINT,
+  enabledManagers: ['docker-compose', 'kubernetes'],
+  kubernetes: {
+    managerFilePatterns: ['/k8s/.+\\.ya?ml$/'],
+  },
+  repositories: (process.env.RENOVATE_REPOSITORIES || '')
+    .split(',')
+    .map((repository) => repository.trim())
+    .filter(Boolean),
+  onboarding: false,
+  requireConfig: 'optional',
+  autodiscover: false,
+  dependencyDashboard: true,
+  prCreation: 'immediate',
+  labels: ['dependencies', 'automated'],
+  extends: [
+    'config:recommended',
+    ':dependencyDashboard',
+  ],
+  packageRules: [
+    {
+      description: 'Do not update private homelab images',
+      matchDatasources: ['docker'],
+      matchPackageNames: ['/gcr\\.forust\\.xyz\\/forust\\/.+/'],
+      enabled: false,
+    },
+    {
+      description: 'Keep major upgrades manual',
+      matchUpdateTypes: ['major'],
+      dependencyDashboardApproval: true,
+      automerge: false,
+    },
+    {
+      description: 'Group patch updates',
+      matchUpdateTypes: ['patch'],
+      groupName: 'container patch updates',
+    },
+  ],
+};