[poison-fountain] opt ingress out of Uptime Kuma external monitor

Deployment is scaled to replicas=0 to silence ExternalAccessDivergence,
but the ingress at poison.viktorbarzin.me was still auto-annotated
`external-monitor=true` by ingress_factory (dns_type=non-proxied path),
so external-monitor-sync kept creating `[External] poison` which
probed a backend with no endpoints and flagged DOWN.

Setting `external_monitor = false` emits the explicit opt-out
annotation; next sync run deleted the orphaned monitor.

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

stacks/poison-fountain/main.tf

@@ -219,6 +219,10 @@ module "ingress" {
   skip_default_rate_limit = true
   exclude_crowdsec        = true
   anti_ai_scraping        = false
+  # Deployment is scaled to 0 (see replicas above). Opt the ingress out of
+  # Uptime Kuma external monitoring so the sync CronJob deletes the orphaned
+  # `[External] poison` monitor instead of flapping DOWN.
+  external_monitor = false
   extra_annotations = {
     "gethomepage.dev/enabled"      = "true"
     "gethomepage.dev/name"         = "Poison Fountain"