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/tenancy/routes/api/merchant.py

@@ -20,9 +20,13 @@ from app.modules.tenancy.schemas import (
     MerchantPortalProfileResponse,
     MerchantPortalProfileUpdate,
     MerchantPortalStoreListResponse,
+    MerchantStoreCreate,
+    MerchantStoreDetailResponse,
+    MerchantStoreUpdate,
 )
 from app.modules.tenancy.schemas.auth import UserContext
 from app.modules.tenancy.services.merchant_service import merchant_service
+from app.modules.tenancy.services.merchant_store_service import merchant_store_service
 
 from .email_verification import email_verification_api_router
 from .merchant_auth import merchant_auth_router
@@ -63,14 +67,113 @@ async def merchant_stores(
         db, merchant.id, skip=skip, limit=limit
     )
 
+    can_create, _ = merchant_store_service.can_create_store(db, merchant.id)
+
     return MerchantPortalStoreListResponse(
         stores=stores,
         total=total,
         skip=skip,
         limit=limit,
+        can_create_store=can_create,
     )
 
 
+@_account_router.post("/stores", response_model=MerchantStoreDetailResponse)
+async def create_merchant_store(
+    store_data: MerchantStoreCreate,
+    current_user: UserContext = Depends(get_current_merchant_api),
+    merchant=Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """
+    Create a new store under the merchant.
+
+    Checks subscription tier store limits before creation.
+    New stores are created with is_active=True, is_verified=False.
+    """
+    # Service raises MaxStoresReachedException, StoreAlreadyExistsException,
+    # or StoreValidationException — all handled by global exception handler.
+    result = merchant_store_service.create_store(
+        db,
+        merchant.id,
+        store_data.model_dump(),
+    )
+    db.commit()
+    logger.info(
+        f"Merchant {merchant.id} ({current_user.username}) created store "
+        f"'{store_data.store_code}'"
+    )
+    return result
+
+
+@_account_router.get("/stores/{store_id}", response_model=MerchantStoreDetailResponse)
+async def get_merchant_store_detail(
+    store_id: int,
+    merchant=Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """
+    Get detailed store information with ownership validation.
+
+    Returns store details including platform assignments.
+    """
+    # StoreNotFoundException handled by global exception handler
+    return merchant_store_service.get_store_detail(db, merchant.id, store_id)
+
+
+@_account_router.put("/stores/{store_id}", response_model=MerchantStoreDetailResponse)
+async def update_merchant_store(
+    store_id: int,
+    update_data: MerchantStoreUpdate,
+    current_user: UserContext = Depends(get_current_merchant_api),
+    merchant=Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """
+    Update store details (merchant-allowed fields only).
+
+    Only name, description, and contact info fields can be updated.
+    """
+    # StoreNotFoundException handled by global exception handler
+    result = merchant_store_service.update_store(
+        db,
+        merchant.id,
+        store_id,
+        update_data.model_dump(exclude_unset=True),
+    )
+    db.commit()
+    logger.info(
+        f"Merchant {merchant.id} ({current_user.username}) updated store {store_id}"
+    )
+    return result
+
+
+@_account_router.get("/platforms")
+async def get_merchant_platforms(
+    merchant=Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """
+    Get platforms available for the merchant (from active subscriptions).
+
+    Used by the store creation/edit UI to show platform selection options.
+    """
+    return merchant_store_service.get_subscribed_platform_ids(db, merchant.id)
+
+
+@_account_router.get("/team")
+async def merchant_team_overview(
+    merchant=Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """
+    Get team members across all stores owned by the merchant.
+
+    Returns a list of stores with their team members grouped by store.
+    """
+    return merchant_store_service.get_merchant_team_overview(db, merchant.id)
+
+
 @_account_router.get("/profile", response_model=MerchantPortalProfileResponse)
 async def merchant_profile(
     request: Request,