fix(k8s): add readiness probes so a bad image cannot look healthy

Six of eight workloads had no readinessProbe, so a pod turned Ready the
moment its process started. The verify job relies on `rollout status`, so
it passed for images that crash-looped or served errors, which left the
rollback safety net inert.

Each probe targets the path the service is actually reached on:
- homepages: / (verified 200)
- error-pages: /404.html, the path Traefik's errorPages middleware
  requests. / returns 403 by design and would never pass.
- webinar-checker: /health (verified 200). /metrics also answers, but it
  is a Prometheus endpoint, not a readiness signal.

The two userbot deployments stay without probes: they expose no port and
no session file, and the panel reaches Telegram through its own client. A
truthful signal there needs a health endpoint in the app itself.

errorpages/k8s/error-pages.yaml

@@ -31,4 +31,11 @@ spec:
           imagePullPolicy: Always
           ports:
             - containerPort: 80
+          readinessProbe:
+            httpGet:
+              path: /404.html
+              port: 80
+            periodSeconds: 10
+            timeoutSeconds: 2
+            failureThreshold: 3
 ---