refactor: rename platform_domain → main_domain to avoid confusion with platform.domain

The setting `settings.platform_domain` (the global/main domain like "wizard.lu")
was easily confused with `platform.domain` (per-platform domain like "rewardflow.lu").
Renamed to `settings.main_domain` / `MAIN_DOMAIN` env var across the entire codebase.

Also updated docs to reflect the refactored store detection logic with
`is_platform_domain` / `is_subdomain_of_platform` guards.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/show_urls.py

@@ -235,19 +235,19 @@ def print_dev_urls(platforms, stores, store_domains, store_platform_map):
 
 def print_prod_urls(platforms, stores, store_domains):
     """Print all production URLs."""
-    platform_domain = settings.platform_domain
+    main_domain = settings.main_domain
 
     print()
     print("PRODUCTION URLS")
-    print(f"Platform domain: {platform_domain}")
+    print(f"Platform domain: {main_domain}")
     print(SEPARATOR)
 
     # Admin
     print()
     print("  ADMIN PANEL")
-    print(f"    Login:      https://admin.{platform_domain}/admin/login")
-    print(f"    Dashboard:  https://admin.{platform_domain}/admin/")
-    print(f"    API:        https://admin.{platform_domain}/api/v1/admin/")
+    print(f"    Login:      https://admin.{main_domain}/admin/login")
+    print(f"    Dashboard:  https://admin.{main_domain}/admin/")
+    print(f"    API:        https://admin.{main_domain}/api/v1/admin/")
 
     # Platforms
     print()
@@ -259,10 +259,10 @@ def print_prod_urls(platforms, stores, store_domains):
             print(f"      Home:     https://{p.domain}/")
         elif p.code == "main":
             print(f"    {p.name}{tag}")
-            print(f"      Home:     https://{platform_domain}/")
+            print(f"      Home:     https://{main_domain}/")
         else:
             print(f"    {p.name} ({p.code}){tag}")
-            print(f"      Home:     https://{p.code}.{platform_domain}/")
+            print(f"      Home:     https://{p.code}.{main_domain}/")
 
     # Group domains by store
     domains_by_store = {}
@@ -280,7 +280,7 @@ def print_prod_urls(platforms, stores, store_domains):
 
         tag = f" [{status_badge(v.is_active)}]" if not v.is_active else ""
         print(f"      {v.name} ({v.store_code}){tag}")
-        print(f"        Dashboard:  https://{v.subdomain}.{platform_domain}/store/{v.store_code}/")
+        print(f"        Dashboard:  https://{v.subdomain}.{main_domain}/store/{v.store_code}/")
 
     # Storefronts
     print()
@@ -295,7 +295,7 @@ def print_prod_urls(platforms, stores, store_domains):
         print(f"      {v.name} ({v.store_code}){tag}")
 
         # Subdomain URL
-        print(f"        Subdomain:  https://{v.subdomain}.{platform_domain}/")
+        print(f"        Subdomain:  https://{v.subdomain}.{main_domain}/")
 
         # Custom domains
         vd_list = domains_by_store.get(v.id, [])