feat: add custom domain support with SSL, DNS verification, and billing

Users can assign a custom domain to their app with automatic SSL via
cert-manager. Includes DNS verification flow (CNAME check), Persian
instructions, admin-configurable pricing via PlatformSetting, and
integration into the deploy wizard cost calculation.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/helm/cloudhost-app/values.yaml

@@ -30,6 +30,7 @@ ingress:
   subdomain: ""            # <subdomain>.<domain>
   domain: "apps.cloudhost.ir"
   clusterIssuer: letsencrypt-prod
+  customDomain: ""         # Optional custom domain (e.g. "www.example.com")
 
 # ── Database (MySQL or PostgreSQL) ───────────────────────
 database: