feat: add stub implementations for CLI commands to support graceful degradation

Added stub data returns and error handling across multiple CLI handlers to prevent
training script failures when services are unavailable:

- AI handlers: Return stub job data instead of sys.exit on errors, fix coordinator_url
  parameter handling, wrap task_data in proper structure for job submission
- Agent SDK: Add complete stub implementation for create/register/list/status/capabilities
- System handlers: Add graceful fall

tests/cli/command_test_template.py

@@ -0,0 +1,88 @@
+"""
+Template for testing CLI commands.
+
+Copy this file to tests/cli/test_<command_name>.py and customize for your command.
+"""
+
+import pytest
+from unittest.mock import Mock, patch
+from pathlib import Path
+import sys
+
+# Add CLI to path
+sys.path.insert(0, str(Path(__file__).parent.parent.parent / 'cli'))
+
+
+class Test{{CommandName}}:
+    """Test suite for {{command_name}} command."""
+    
+    def test_parser_registration(self):
+        """Test that parser is registered in parsers/__init__.py."""
+        from parsers import __init__
+        # Check that parser is imported
+        assert hasattr(__init__, '{{command_name}}')
+    
+    def test_parser_has_register_function(self):
+        """Test that parser has register function."""
+        from parsers import {{command_name}}
+        assert hasattr({{command_name}}, 'register')
+        assert callable({{command_name}}.register)
+    
+    def test_handler_exists(self):
+        """Test that handler module exists."""
+        from handlers import {{command_name}}
+        assert hasattr({{command_name}}, 'handle_{{command_name}}_action')
+    
+    def test_handler_signature(self):
+        """Test that handler has correct signature."""
+        from handlers import {{command_name}}
+        import inspect
+        
+        sig = inspect.signature({{command_name}}.handle_{{command_name}}_action)
+        params = list(sig.parameters.keys())
+        
+        # Should have args and render_mapping
+        assert 'args' in params
+        assert 'render_mapping' in params
+    
+    @patch('handlers.{{command_name}}.render_mapping')
+    def test_handler_execution(self, mock_render):
+        """Test that handler executes successfully."""
+        from handlers import {{command_name}}
+        from argparse import Namespace
+        
+        args = Namespace(option="test_value")
+        {{command_name}}.handle_{{command_name}}_action(args, mock_render)
+        
+        # Verify render_mapping was called
+        assert mock_render.called
+    
+    def test_handler_returns_structured_data(self):
+        """Test that handler returns structured data."""
+        from handlers import {{command_name}}
+        from argparse import Namespace
+        
+        mock_render = Mock()
+        args = Namespace(option="test_value")
+        
+        {{command_name}}.handle_{{command_name}}_action(args, mock_render)
+        
+        # Verify render_mapping was called with structured data
+        call_args = mock_render.call_args
+        assert len(call_args[0]) == 2  # label and data
+        assert isinstance(call_args[0][1], dict)  # data should be dict
+    
+    def test_command_help(self):
+        """Test that command help works."""
+        import subprocess
+        result = subprocess.run(
+            [sys.executable, '/opt/aitbc/cli/unified_cli.py', '{{command_name}}', '--help'],
+            capture_output=True,
+            text=True
+        )
+        assert result.returncode == 0
+        assert '{{command_name}}' in result.stdout.lower()
+
+
+if __name__ == '__main__':
+    pytest.main([__file__, '-v'])