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/_helpers.tpl

@@ -35,7 +35,8 @@ Usage: {{ include "ezscale-website.image" (dict "ctx" . "role" "app") }}
 */}}
 {{- define "ezscale-website.image" -}}
 {{- $ctx := .ctx -}}
-{{- printf "%s/%s:%s-%s" $ctx.Values.image.registry $ctx.Values.image.repository .role $ctx.Values.image.tag -}}
+{{- $tag := required "image.tag is required (set via --set image.tag=vX.Y.Z)" $ctx.Values.image.tag -}}
+{{- printf "%s/%s:%s-%s" $ctx.Values.image.registry $ctx.Values.image.repository .role $tag -}}
 {{- end -}}
 
 {{/* Secret name (existing or generated) */}}