fix(helm): hardening from review

- _helpers.tpl: required guard on image.tag — silent empty deploys can
  no longer happen; helm fails fast with a clear message.
- configmap-nginx: HTTPS fastcgi param uses if_not_empty, so PHP only
  sees HTTPS when X-Forwarded-Proto is actually present.
- deployment-app: add startupProbe with 100s budget so first-boot cache
  warmup doesn't trip liveness.
- deployment-horizon: failureThreshold=5 on the horizon:status probe;
  transient Valkey blips no longer cause restart loops.
- job-migrate: mount oauth-keys so seeders that touch Passport clients
  don't silently fail.
- statefulset-valkey: replace separate password Secret with a
  requirePassword toggle that reads REDIS_PASSWORD from the main chart
  Secret (same Secret app/horizon/scheduler already mount). Liveness
  probe authenticates with the password when set.
- values-us-prod: enable valkey.requirePassword.
- README: add REDIS_PASSWORD to bootstrap procedure.

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

helm/ezscale-website/templates/deployment-horizon.yaml

@@ -41,6 +41,8 @@ spec:
               readOnly: true
           resources:
             {{- toYaml .Values.horizon.resources | nindent 12 }}
+          # horizon:status hits Redis. failureThreshold: 5 + periodSeconds: 30
+          # gives 150s of tolerance for transient Valkey blips before restart.
           livenessProbe:
             exec:
               command:
@@ -50,6 +52,7 @@ spec:
             initialDelaySeconds: 30
             periodSeconds: 30
             timeoutSeconds: 10
+            failureThreshold: 5
       volumes:
         - name: oauth-keys
           secret: