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/models/customer.py

@@ -10,10 +10,8 @@ from sqlalchemy import (
     JSON,
     Boolean,
     Column,
-    DateTime,
     ForeignKey,
     Integer,
-    Numeric,
     String,
 )
 from sqlalchemy.orm import relationship
@@ -41,9 +39,6 @@ class Customer(Base, TimestampMixin):
     )  # Store-specific ID
     preferences = Column(JSON, default=dict)
     marketing_consent = Column(Boolean, default=False)
-    last_order_date = Column(DateTime)
-    total_orders = Column(Integer, default=0)
-    total_spent = Column(Numeric(10, 2), default=0)
     is_active = Column(Boolean, default=True, nullable=False)
 
     # Language preference (NULL = use store storefront_language default)