add marketing-dev environment - team-internal auto-deploy zone

dev.neurontechnologies.ai mirrors stage in shape but looser:
broken builds OK, auto-deploys on every push to dev branch (once
CI lands), dev Supabase project (isolated), test Stripe keys,
RESEND_DRY_RUN=1 so transactional email never actually sends.

Locked behind Cloudflare Access with team policy: anyone with
@neurontechnologies.ai email plus named external collaborators
via the access app's emails list.

Initial image is marketing:fix-gallery-render-1236 (matches stage
at the time of this commit). Future deploys land via CI workflow.

servers/legion/dns-neurontechnologies.tf

@@ -43,14 +43,12 @@ resource "cloudflare_record" "nt_tunnel_www" {
   ttl     = 1
 }
 
-resource "cloudflare_record" "nt_tunnel_dev" {
-  zone_id = local.zone_neurontechnologies_ai
-  name    = "dev"
-  type    = "CNAME"
-  content = "${var.cloudflare_tunnel_id}.cfargotunnel.com"
-  proxied = true
-  ttl     = 1
-}
+# dev.neurontechnologies.ai DNS moved to servers/gcp/marketing-dev.tf
+# (Cloud Run-fronted marketing dev environment). The legion-side
+# neuron-dev namespace + ingress + tunnel ingress_rule remain in place
+# but no longer receive traffic - they're inert until a follow-up
+# decision retires them or rehosts under mcp-dev.neurontechnologies.ai.
+# See backlog: "Retire or rehost legion neuron-dev namespace".
 
 resource "cloudflare_record" "nt_tunnel_stage" {
   zone_id = local.zone_neurontechnologies_ai