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/merchant/partials/header.html

@@ -31,10 +31,11 @@
                 <button
                     @click="isLangOpen = !isLangOpen"
                     @click.outside="isLangOpen = false"
-                    class="p-1 rounded-md focus:outline-none focus:shadow-outline-purple"
+                    class="inline-flex items-center gap-1 p-1 rounded-md focus:outline-none focus:shadow-outline-purple"
                     aria-label="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 text-gray-600 dark:text-gray-300 uppercase" x-text="currentLang"></span>
                 </button>
                 <div
                     x-show="isLangOpen"

app/templates/merchant/partials/sidebar.html

@@ -52,7 +52,13 @@
                             @click="toggleSection(section.id)"
                             class="flex items-center justify-between w-full px-6 py-2 text-xs font-semibold text-gray-600 dark:text-gray-400 uppercase tracking-wider hover:bg-gray-50 dark:hover:bg-gray-700/50 transition-colors"
                         >
-                            <span class="flex items-center" x-text="section.label"></span>
+                            <span class="flex items-center">
+                                <span x-show="section.icon" x-html="$icon(section.icon, 'w-4 h-4 mr-2')" class="opacity-60"></span>
+                                <span x-text="section.label"></span>
+                                <span x-show="section.platform_code"
+                                      class="ml-2 px-1.5 py-0.5 text-[10px] font-medium rounded bg-purple-100 text-purple-700 dark:bg-purple-900 dark:text-purple-300 normal-case"
+                                      x-text="section.platform_code?.toUpperCase()"></span>
+                            </span>
                             <span
                                 x-html="$icon('chevron-down', 'w-4 h-4 transition-transform duration-200')"
                                 :class="{ 'rotate-180': openSections[section.id] }"