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/tests/unit/test_menu_service.py

@@ -110,3 +110,62 @@ class TestMenuServiceMerchantRendering:
         without_ids = {s.id for s in without_loyalty}
         assert "loyalty" in with_ids
         assert "loyalty" not in without_ids
+
+
+@pytest.mark.unit
+@pytest.mark.core
+class TestMenuServiceMerchantByPlatform:
+    """Test get_merchant_menu_by_platform grouping logic."""
+
+    def setup_method(self):
+        self.service = MenuService()
+
+    def test_core_sections_contain_only_core_items(self, db):
+        """Core sections should only have items from core modules."""
+        from app.modules.core.services.menu_discovery_service import (
+            menu_discovery_service,
+        )
+        from app.modules.registry import MODULES
+
+        core_codes = {code for code, mod in MODULES.items() if mod.is_core}
+
+        core_sections = menu_discovery_service.get_menu_sections_for_frontend(
+            db,
+            FrontendType.MERCHANT,
+            enabled_module_codes=core_codes,
+        )
+        for section in core_sections:
+            section.items = [i for i in section.items if i.module_code in core_codes]
+
+        for section in core_sections:
+            for item in section.items:
+                assert item.module_code in core_codes, (
+                    f"Non-core item '{item.id}' (module={item.module_code}) "
+                    f"found in core section '{section.id}'"
+                )
+
+    def test_non_core_sections_for_loyalty(self, db):
+        """Non-core modules like loyalty produce merchant menu sections."""
+        from app.modules.core.services.menu_discovery_service import (
+            menu_discovery_service,
+        )
+        from app.modules.registry import MODULES
+
+        core_codes = {code for code, mod in MODULES.items() if mod.is_core}
+        non_core = {"loyalty"}
+
+        sections = menu_discovery_service.get_menu_sections_for_frontend(
+            db,
+            FrontendType.MERCHANT,
+            enabled_module_codes=non_core,
+        )
+        sections = [
+            s
+            for s in sections
+            if any(i.module_code in non_core for i in s.items)
+        ]
+
+        assert len(sections) > 0, "Loyalty module should produce merchant menu sections"
+        for section in sections:
+            for item in section.items:
+                assert item.module_code not in core_codes