refactor(theme): drop dark-green and collapse theme registry to light/dark

Remove the extensible theme catalog (config/themes.php + ThemeConfigGateway)
in favor of a two-entry const on SettingsAppGateway. appThemes() now returns
the list directly — no container lookup, no file include. Drop the
dark-green theme assets, narrow [data-theme^="dark"] selectors to
[data-theme="dark"], and tighten isDarkTheme() to an exact match. Ship an
idempotent migration that corrects any leftover 'dark-green' rows on users
and tenants to safe defaults (light / NULL).

Tenant scoping (default_theme, allow_user_theme) and per-user override stay
intact; only the catalog extensibility and the third theme are removed.

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

core/Service/Settings/SettingServicesFactory.php

@@ -9,7 +9,6 @@ use MintyPHP\Repository\Tenant\TenantRepositoryInterface;
 
 class SettingServicesFactory
 {
-    private ?ThemeConfigGateway $themeConfigService = null;
     private ?SettingCacheService $settingCacheService = null;
     private ?SettingsCryptoGatewayInterface $settingsCryptoGateway = null;
     private ?SettingsMetadataGateway $settingsMetadataGateway = null;
@@ -53,7 +52,6 @@ class SettingServicesFactory
     {
         return $this->settingsAppGateway ??= new SettingsAppGateway(
             $this->createSettingsMetadataGateway(),
-            $this->createThemeConfigGateway(),
         );
     }
 
@@ -108,11 +106,6 @@ class SettingServicesFactory
         );
     }
 
-    public function createThemeConfigGateway(): ThemeConfigGateway
-    {
-        return $this->themeConfigService ??= new ThemeConfigGateway();
-    }
-
     public function createSettingsCryptoGateway(): SettingsCryptoGatewayInterface
     {
         return $this->settingsCryptoGateway ??= new SettingsCryptoGateway();