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/core/models/admin_menu_config.py

@@ -100,12 +100,15 @@ class AdminMenuConfig(Base, TimestampMixin):
         comment="Platform scope - applies to users/stores of this platform",
     )
 
+    # DEPRECATED: user_id scoping is no longer used. Super admins now use platform
+    # selection instead of personal menu config. DB migration to drop this column
+    # is a separate task.
     user_id = Column(
         Integer,
         ForeignKey("users.id", ondelete="CASCADE"),
         nullable=True,
         index=True,
-        comment="User scope - applies to this specific super admin (admin frontend only)",
+        comment="DEPRECATED - User scope no longer used. Kept for migration compatibility.",
     )
 
     # ========================================================================