Fix socketio mocking and add MODEL_ENDPOINT env vars for tests

Fixed remaining 2 integration test failures:

1. Socketio mocking issue:
   - Tests were setting app.socketio but activity module has its own reference
   - Fixed by mocking activity.socketio directly instead of app.socketio
   - Updated test_cancel_activity_integration to check both chat_message and activity_status events
   - Updated test_display_activity_metadata_integration to use activity.socketio

2. GitHub Actions environment variables:
   - Added MODEL_ENDPOINT_0 and MODEL_API_KEY_0 to all test steps
   - These are required for app.py initialization
   - Set to dummy values (https://test.api) for testing

Test Results:
- Before: 2 failed, 39 passed
- After: 41 passed ✅

All integration tests now pass locally and should pass on GitHub Actions.

.github/workflows/test.yml

@@ -37,6 +37,8 @@ jobs:
       env:
         SQLALCHEMY_DATABASE_URI: "sqlite:///:memory:"
         TESTING: "1"
+        MODEL_ENDPOINT_0: "https://test.api"
+        MODEL_API_KEY_0: "test-key"
 
     - name: Run functional tests
       run: |
@@ -44,6 +46,8 @@ jobs:
       env:
         SQLALCHEMY_DATABASE_URI: "sqlite:///:memory:"
         TESTING: "1"
+        MODEL_ENDPOINT_0: "https://test.api"
+        MODEL_API_KEY_0: "test-key"
 
     - name: Run integration tests
       run: |
@@ -51,6 +55,8 @@ jobs:
       env:
         SQLALCHEMY_DATABASE_URI: "sqlite:///:memory:"
         TESTING: "1"
+        MODEL_ENDPOINT_0: "https://test.api"
+        MODEL_API_KEY_0: "test-key"
 
     - name: Validate activity YAML files
       run: |