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/routes/pages/store.py

@@ -44,3 +44,25 @@ async def store_customers_page(
         "customers/store/customers.html",
         get_store_context(request, db, current_user, store_code),
     )
+
+
+@router.get(
+    "/customers/{customer_id}", response_class=HTMLResponse, include_in_schema=False
+)
+async def store_customer_detail_page(
+    request: Request,
+    customer_id: int,
+    store_code: str = Depends(get_resolved_store_code),
+    current_user: User = Depends(require_store_page_permission("customers.view")),
+    db: Session = Depends(get_db),
+):
+    """
+    Render customer detail page.
+    JavaScript loads customer profile and order stats via API.
+    """
+    context = get_store_context(request, db, current_user, store_code)
+    context["customer_id"] = customer_id
+    return templates.TemplateResponse(
+        "customers/store/customer-detail.html",
+        context,
+    )