refactor(sdk): rename SubagentEvent.task_tool_call_id to parent_tool_call_id

[tempurai]

Summary

• Rename SubagentEvent.task_tool_call_id to parent_tool_call_id across schema, tests, README, and webview consumer
• Add error logging around CLI install and verification in the VS Code extension
• Bump vscode_extension to 0.4.7

Test plan

• pnpm test in node/agent_sdk passes
• Subagent events still resolve to the correct parent tool-use item in the webview
• CLI install/verify failure paths surface useful error logs