test: add tests for merchant dashboard metrics and fix invoice template location

Move invoice PDF template from app/templates/invoices/ to
app/modules/orders/templates/invoices/ where InvoicePDFService expects it.
Expand invoice PDF tests to validate template path and existence.

Add unit tests for get_merchant_metrics() in tenancy, billing, and
customer metrics providers. Add unit tests for StatsAggregatorService
merchant methods. Add integration tests for the merchant dashboard
stats endpoint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/customers/tests/unit/test_customer_metrics.py

@@ -0,0 +1,130 @@
+# app/modules/customers/tests/unit/test_customer_metrics.py
+"""Unit tests for CustomerMetricsProvider.get_merchant_metrics."""
+
+import uuid
+
+import pytest
+
+from app.modules.customers.models.customer import Customer
+from app.modules.customers.services.customer_metrics import CustomerMetricsProvider
+from app.modules.tenancy.models import Merchant, Store, User
+
+
+@pytest.fixture
+def cust_merchant(db):
+    """Create a merchant for customer metrics tests."""
+    from middleware.auth import AuthManager
+
+    auth = AuthManager()
+    user = User(
+        email=f"custowner_{uuid.uuid4().hex[:8]}@test.com",
+        username=f"custowner_{uuid.uuid4().hex[:8]}",
+        hashed_password=auth.hash_password("pass123"),
+        role="merchant_owner",
+        is_active=True,
+    )
+    db.add(user)
+    db.flush()
+
+    merchant = Merchant(
+        name="Customer Metrics Merchant",
+        owner_user_id=user.id,
+        contact_email=user.email,
+        is_active=True,
+        is_verified=True,
+    )
+    db.add(merchant)
+    db.commit()
+    db.refresh(merchant)
+    return merchant
+
+
+@pytest.fixture
+def cust_stores(db, cust_merchant):
+    """Create 2 stores for the merchant."""
+    stores = []
+    for i in range(2):
+        uid = uuid.uuid4().hex[:8].upper()
+        store = Store(
+            merchant_id=cust_merchant.id,
+            store_code=f"CSTORE_{uid}",
+            subdomain=f"cstore{uid.lower()}",
+            name=f"Cust Store {i}",
+            is_active=True,
+            is_verified=True,
+        )
+        db.add(store)
+        stores.append(store)
+    db.commit()
+    for s in stores:
+        db.refresh(s)
+    return stores
+
+
+@pytest.fixture
+def cust_customers(db, cust_stores):
+    """Create customers across the merchant's stores."""
+    customers = []
+    # 3 customers in store 0
+    for i in range(3):
+        uid = uuid.uuid4().hex[:8]
+        c = Customer(
+            store_id=cust_stores[0].id,
+            email=f"cust_{uid}@test.com",
+            hashed_password="hashed",  # noqa: SEC001
+            first_name=f"First{i}",
+            last_name=f"Last{i}",
+            customer_number=f"C{uid}",
+            is_active=True,
+        )
+        db.add(c)
+        customers.append(c)
+    # 2 customers in store 1
+    for i in range(2):
+        uid = uuid.uuid4().hex[:8]
+        c = Customer(
+            store_id=cust_stores[1].id,
+            email=f"cust_{uid}@test.com",
+            hashed_password="hashed",  # noqa: SEC001
+            first_name=f"First{i}",
+            last_name=f"Last{i}",
+            customer_number=f"C{uid}",
+            is_active=True,
+        )
+        db.add(c)
+        customers.append(c)
+    db.commit()
+    return customers
+
+
+@pytest.mark.unit
+@pytest.mark.customers
+class TestCustomerMetricsProviderMerchant:
+    """Tests for CustomerMetricsProvider.get_merchant_metrics."""
+
+    def setup_method(self):
+        self.provider = CustomerMetricsProvider()
+
+    def test_total_customers_across_stores(self, db, cust_merchant, cust_stores, cust_customers):
+        """Aggregates customers across all merchant stores."""
+        metrics = self.provider.get_merchant_metrics(db, cust_merchant.id)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["customers.total"] == 5
+
+    def test_no_customers(self, db, cust_merchant, cust_stores):
+        """Returns zero when stores have no customers."""
+        metrics = self.provider.get_merchant_metrics(db, cust_merchant.id)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["customers.total"] == 0
+
+    def test_no_stores(self, db, cust_merchant):
+        """Returns zero when merchant has no stores."""
+        metrics = self.provider.get_merchant_metrics(db, cust_merchant.id)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["customers.total"] == 0
+
+    def test_nonexistent_merchant(self, db):
+        """Returns zero for a non-existent merchant ID."""
+        metrics = self.provider.get_merchant_metrics(db, 999999)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["customers.total"] == 0