renovate: set minimumReleaseAgeBehaviour=timestamp-optional

Debug dry-run revealed why termix (and reloader/homepage/headlamp
8d ago) sit in "Pending Status Checks" indefinitely:

  Marking 2 release(s) as pending, as they do not have a
  releaseTimestamp and we're running with
  minimumReleaseAgeBehaviour=timestamp-required
  "depName": "ghcr.io/lukegus/termix"
  "versions": ["release-1.11.2", "release-1.11.1"]
  "check": "minimumReleaseAge"

ghcr.io OCI manifests for these images don't expose a release
timestamp Renovate can read, so the default `timestamp-required`
mode turns the 3-day stability gate into an INFINITE hold for
ghcr.io packages -- silently. PRs are never opened.

Switching to `timestamp-optional` (other supported value per Renovate
source: lib/config/options/index.ts) makes the gate best-effort: the
3-day window is still enforced for any package the datasource gives a
timestamp for; packages without a timestamp are allowed through.
Restores intended behavior.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

admin-system/renovate.yaml

@@ -46,6 +46,7 @@ data:
       "dependencyDashboardTitle": "Renovate Dependency Dashboard",
       "prHourlyLimit": 8,
       "prConcurrentLimit": 8,
+      "minimumReleaseAgeBehaviour": "timestamp-optional",
       "enabledManagers": ["kubernetes", "helm-values"],
       "kubernetes": {
         "managerFilePatterns": ["/.+\\.ya?ml$/"]