🧹 Refactor ToolRegistry to dynamically identify final answer tools

[KeithCu]

🎯 What: The code health issue addressed
Removed the hardcoded list of strings (["final_answer", "specialized_workflow_finished", "reply_to_user"]) in plugin/framework/tool_registry.py and replaced it with a dynamic boolean check getattr(t, "is_final_answer_tool", False). Added is_final_answer_tool = False to ToolBase and overrode it as True in the SpecializedWorkflowFinished tool.

💡 Why: How this improves maintainability
This prevents the ToolRegistry from needing to know the specific names of final answer tools across different domains. Hardcoding class names/identifiers in a central registry makes adding new tools brittle and couples the registry to specific features (e.g. Writer specialized tools, Librarian). By using a boolean flag, tools can self-declare their role in the workflow.

✅ Verification: How you confirmed the change is safe
Ran uv run ty check plugin/framework/tool_registry.py to verify type safety. Ran the full pytest suite (uv run pytest plugin/tests/) and confirmed all tests pass without introducing new failures. Validated that reply_to_user and final_answer are handled dynamically as final_answer_tool_name parameters within smolagents and thus never needed to be in the ToolBase list anyway.

✨ Result: The improvement achieved
A cleaner, decoupled ToolRegistry that scales safely with new tools and cleanly relies on properties of the ToolBase hierarchy.

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PR created automatically by Jules for task 9247852521992975344 started by @KeithCu

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