refactor(agents): migrate 3 agents to StandardizedAgent base class (#3387)

[mrveiss]

Summary

Migrated 3 high-priority agents to inherit from StandardizedAgent base class:

• JSONFormatterAgent — JSON parsing utility (parse, validate actions)
• InteractiveTerminalAgent — PTY/terminal wrapper (start session, send input, signals)
• SystemCommandAgent — Command execution wrapper (execute, install tools, validate)

Changes

• Added StandardizedAgent base class inheritance to all 3 agents
• Registered action handlers for each agent's primary operations
• Implemented _get_system_prompt() and get_capabilities() abstract methods
• Preserved all existing public methods and module-level singletons for backward compatibility
• Integrated with StandardizedAgent's error handling and performance tracking

Migration Pattern

All 3 agents now follow the standard pattern:

class MyAgent(StandardizedAgent):
    def __init__(self):
        super().__init__("agent_type_id")
        self.register_actions({
            "action_name": ActionHandler(handler_method="handle_action", ...)
        })
    
    async def handle_action(self, request: AgentRequest) -> Any:
        # Action handler implementation
        return result
    
    def _get_system_prompt(self) -> str:
        return "agent system prompt"
    
    def get_capabilities(self) -> List[str]:
        return ["capability1", "capability2"]

Remaining Work

20+ agents remain to be migrated in follow-up PRs. Complex agents (HierarchicalAgent, OverseerAgent, StepExecutorAgent) should be handled separately due to intricate task delegation logic.

Test Plan

• Code syntax verified
• Existing methods preserved
• Action handlers properly registered
• Integration tests (existing test suite)

Closes #3387

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