added opencode zen as provider

tests/conftest.py

@@ -82,9 +82,20 @@ def project_path(tmp_path):
     return test_dir
 
 
+@pytest.fixture
+def zen_provider():
+    """
+    Provides a Zen provider instance for testing.
+    Uses dummy API key for isolated testing.
+    """
+    from providers.zen import ZenProvider
+
+    return ZenProvider(api_key="test-zen-key")
+
+
 def _set_dummy_keys_if_missing():
     """Set dummy API keys only when they are completely absent."""
-    for var in ("GEMINI_API_KEY", "OPENAI_API_KEY", "XAI_API_KEY"):
+    for var in ("GEMINI_API_KEY", "OPENAI_API_KEY", "XAI_API_KEY", "ZEN_API_KEY"):
         if not os.environ.get(var):
             os.environ[var] = "dummy-key-for-tests"