feat: add marketplace products admin UI with copy-to-vendor functionality

- Add admin marketplace products page to browse imported products
- Add admin vendor products page to manage vendor catalog
- Add product detail pages for both marketplace and vendor products
- Implement copy-to-vendor API to copy marketplace products to vendor catalogs
- Add vendor product service with CRUD operations
- Update sidebar navigation with new product management links
- Add integration and unit tests for new endpoints and services

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/fixtures/auth_fixtures.py

@@ -92,23 +92,22 @@ def other_user(db, auth_manager):
 
 
 @pytest.fixture
-def auth_headers(client, test_user):
-    """Get authentication headers for test user"""
-    response = client.post(
-        "/api/v1/auth/login",
-        json={"username": test_user.username, "password": "testpass123"},
-    )
-    assert response.status_code == 200, f"Login failed: {response.text}"
-    token = response.json()["access_token"]
-    return {"Authorization": f"Bearer {token}"}
+def auth_headers(test_user, auth_manager):
+    """Get authentication headers for test user (non-admin).
+
+    Uses direct JWT generation to avoid vendor context requirement of shop login.
+    This is used for testing non-admin access to admin endpoints.
+    """
+    token_data = auth_manager.create_access_token(user=test_user)
+    return {"Authorization": f"Bearer {token_data['access_token']}"}
 
 
 @pytest.fixture
 def admin_headers(client, test_admin):
     """Get authentication headers for admin user"""
     response = client.post(
-        "/api/v1/auth/login",
-        json={"username": test_admin.username, "password": "adminpass123"},
+        "/api/v1/admin/auth/login",
+        json={"email_or_username": test_admin.username, "password": "adminpass123"},
     )
     assert response.status_code == 200, f"Admin login failed: {response.text}"
     token = response.json()["access_token"]
@@ -137,8 +136,8 @@ def test_vendor_user(db, auth_manager):
 def vendor_user_headers(client, test_vendor_user):
     """Get authentication headers for vendor user (uses get_current_vendor_api)"""
     response = client.post(
-        "/api/v1/auth/login",
-        json={"username": test_vendor_user.username, "password": "vendorpass123"},
+        "/api/v1/vendor/auth/login",
+        json={"email_or_username": test_vendor_user.username, "password": "vendorpass123"},
     )
     assert response.status_code == 200, f"Vendor login failed: {response.text}"
     token = response.json()["access_token"]