feat: multi-module improvements across merchant, store, i18n, and customer systems

- Fix platform-grouped merchant sidebar menu with core items at root level
- Add merchant store management (detail page, create store, team page)
- Fix store settings 500 error by removing dead stripe/API tab
- Move onboarding translations to module-owned locale files
- Fix onboarding banner i18n with server-side rendering + context inheritance
- Refactor login language selectors to use languageSelector() function (LANG-002)
- Move HTTPException handling to global exception handler in merchant routes (API-003)
- Add language selector to all login pages and portal headers
- Fix customer module: drop order stats from customer model, add to orders module
- Fix admin menu config visibility for super admin platform context
- Fix storefront auth and layout issues
- Add missing i18n translations for onboarding steps (en/fr/de/lb)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/shared/macros/feature_gate.html

@@ -355,13 +355,13 @@
         <div class="flex items-center justify-between">
             <div class="flex items-center gap-3">
                 <span x-html="$icon('rocket', 'w-5 h-5 text-purple-600 dark:text-purple-400')"></span>
-                <h3 class="text-lg font-semibold text-gray-900 dark:text-white" x-text="t('onboarding.banner.title')">Get Started</h3>
+                <h3 class="text-lg font-semibold text-gray-900 dark:text-white">{{ _("onboarding.banner.title") }}</h3>
                 <span class="text-sm text-gray-500 dark:text-gray-400"
                       x-text="`${completedSteps}/${totalSteps}`"></span>
             </div>
             <button @click="dismiss()"
                     class="text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 transition-colors"
-                    :title="t('onboarding.banner.dismiss')">
+                    title="{{ _("onboarding.banner.dismiss") }}">
                 <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                     <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
                 </svg>

app/templates/shared/macros/language_selector.html

@@ -69,7 +69,8 @@
         class="inline-flex items-center gap-2 px-3 py-2 text-sm font-medium text-gray-700 dark:text-gray-300 bg-white dark:bg-gray-800 border border-gray-300 dark:border-gray-600 rounded-lg hover:bg-gray-50 dark:hover:bg-gray-700 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-purple-500 transition-colors"
         :class="{ 'ring-2 ring-purple-500 ring-offset-2': isLangOpen }"
     >
-        <span class="fi" :class="'fi-' + languageFlags[currentLang]"></span>
+        <span x-html="$icon('globe-alt', 'w-5 h-5')"></span>
+        <span class="text-xs font-semibold uppercase" x-text="currentLang"></span>
         {% if show_label %}
         <span x-text="languageNames[currentLang]" class="hidden sm:inline"></span>
         {% endif %}
@@ -130,11 +131,12 @@
         @click="isLangOpen = !isLangOpen"
         @click.outside="isLangOpen = false"
         type="button"
-        class="p-2 text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 hover:bg-gray-100 dark:hover:bg-gray-700 rounded-lg transition-colors focus:outline-none"
+        class="inline-flex items-center gap-1 p-2 text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 hover:bg-gray-100 dark:hover:bg-gray-700 rounded-lg transition-colors focus:outline-none"
         :class="{ 'text-gray-700 dark:text-white bg-gray-100 dark:bg-gray-700': isLangOpen }"
         title="Change language"
     >
-        <span class="fi text-lg" :class="'fi-' + languageFlags[currentLang]"></span>
+        <span x-html="$icon('globe-alt', 'w-5 h-5')"></span>
+        <span class="text-xs font-semibold uppercase" x-text="currentLang"></span>
     </button>
 
     <div