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/modules/tenancy/locales/de.json

@@ -144,5 +144,11 @@
         "team_edit_desc": "Rollen und Berechtigungen der Mitglieder bearbeiten",
         "team_remove": "Mitglieder entfernen",
         "team_remove_desc": "Mitglieder aus dem Team entfernen"
+    },
+    "onboarding": {
+        "customize_store": {
+            "title": "Shop anpassen",
+            "description": "Fügen Sie eine Beschreibung und ein Logo hinzu"
+        }
     }
 }