fix: stabilize todo_write rendering while streaming

[nonoroazoro]

Summary

• keep the specialized todo_write view mounted while tool arguments stream
• render only complete todo items and preserve the cancelled status
• isolate todo input parsing, remove duplicate argument preview work, and stabilize row rendering

Testing

• bun test (364 passed)
• bun run lint
• bun run typecheck
• verified stable DOM reuse across partial updates in the Electrobun CEF renderer