Fix Google ADK extension documentation and linting config

[Copilot]

Addresses review feedback on PR #156 for the Google ADK tooling extension.

Changes

• Removed agentic_app_id from documentation - This parameter doesn't exist in add_tool_servers_to_agent(). It's derived internally via Utility.resolve_agent_identity(context, auth_token). Removed from both the example code and parameter table in design.md.

• Added ruff copyright linting config - Missing [tool.ruff.lint.flake8-copyright] section in pyproject.toml, now consistent with other tooling extension packages.

Corrected Usage

# Before (incorrect)
agent = await service.add_tool_servers_to_agent(
    agent=existing_agent,
    agentic_app_id="your-agent-id",  # ❌ doesn't exist
    auth=auth_context,
    context=turn_context,
)

# After (correct)
agent = await service.add_tool_servers_to_agent(
    agent=existing_agent,
    auth=auth_context,
    auth_handler_name="graph",
    context=turn_context,
)

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