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/customers/schemas/customer.py

@@ -111,9 +111,6 @@ class CustomerResponse(BaseModel):
     customer_number: str
     marketing_consent: bool
     preferred_language: str | None
-    last_order_date: datetime | None
-    total_orders: int
-    total_spent: Decimal
     is_active: bool
     created_at: datetime
     updated_at: datetime
@@ -291,10 +288,6 @@ class CustomerStatisticsResponse(BaseModel):
     total: int = 0
     active: int = 0
     inactive: int = 0
-    with_orders: int = 0
-    total_spent: float = 0.0
-    total_orders: int = 0
-    avg_order_value: float = 0.0
 
 
 # ============================================================================
@@ -314,9 +307,6 @@ class AdminCustomerItem(BaseModel):
     customer_number: str
     marketing_consent: bool = False
     preferred_language: str | None = None
-    last_order_date: datetime | None = None
-    total_orders: int = 0
-    total_spent: float = 0.0
     is_active: bool = True
     created_at: datetime
     updated_at: datetime