Add credits to account in test setup for content generation, linking, and optimization tests

- Updated test cases in `test_universal_content_types.py`, `test_universal_content_linking.py`, and `test_universal_content_optimization.py` to initialize account credits for testing.
- Changed mock patch references to `run_ai_task` for consistency across tests.

backend/igny8_core/business/optimization/tests/test_universal_content_optimization.py

@@ -15,6 +15,9 @@ class UniversalContentOptimizationTests(IntegrationTestBase):
     
     def setUp(self):
         super().setUp()
+        # Add credits to account for testing
+        self.account.credits = 10000
+        self.account.save()
         self.optimizer_service = OptimizerService()
         
         # Create product content