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>

static/locales/lb.json

@@ -111,7 +111,35 @@
     "invalid_credentials": "Ongëltege Benotzernumm oder Passwuert",
     "session_expired": "Är Sessioun ass ofgelaf. Mellt Iech w.e.g. erëm un.",
     "account_locked": "Äre Kont ass gespaart",
-    "account_inactive": "Äre Kont ass inaktiv"
+    "account_inactive": "Äre Kont ass inaktiv",
+    "signing_in": "Umellen...",
+    "sending": "Gëtt geschéckt...",
+    "send_reset_link": "Link fir zréckzesetzen schécken",
+    "reset_password_desc": "Gitt Är E-Mail-Adress an a mir schécken Iech e Link fir Äert Passwuert zréckzesetzen.",
+    "back_to_login": "Zréck zum Login",
+    "back_to_platform": "Zréck zur Plattform",
+    "no_account": "Kee Kont?",
+    "visit_platform": "Besicht eis Plattform",
+    "already_have_account": "Hutt Dir schonn e Kont?",
+    "create_account": "E Kont erstellen",
+    "continue_shopping": "Weider akafen",
+    "admin_login": "Admin Login",
+    "merchant_login": "Händler Login",
+    "store_login": "Buttek-Portal Login",
+    "customer_login": "Client Login",
+    "create_account_title": "Kont erstellen",
+    "creating_account": "Kont gëtt erstallt...",
+    "sign_in_instead": "Aloggen amplaz",
+    "first_name": "Virnumm",
+    "last_name": "Nonumm",
+    "phone_number": "Telefonsnummer",
+    "marketing_consent": "Ech wëll Neiegkeeten an Spezialangebotter kréien",
+    "password_requirements": "Muss mindestens 8 Zeechen, ee Buschtaf an eng Zuel enthalen",
+    "check_email": "Kuckt Är E-Mail",
+    "reset_link_sent": "Mir hunn e Link fir d'Passwuert zréckzesetzen op Är E-Mail-Adress geschéckt. Kuckt w.e.g. Ären Posteingang a klickt op de Link.",
+    "didnt_receive_email": "E-Mail net kritt? Kuckt Ären Spam-Dossier oder",
+    "try_again": "probéiert et nach eng Kéier",
+    "remember_password": "Passwuert erëm agefall?"
   },
   "nav": {
     "dashboard": "Dashboard",
@@ -191,5 +219,11 @@
     "time": "HH:mm",
     "datetime": "DD.MM.YYYY HH:mm",
     "currency": "{amount} {symbol}"
+  },
+  "onboarding": {
+    "banner": {
+      "title": "Ufänken",
+      "dismiss": "Verstoppen"
+    }
   }
 }