Build CLI recorder MVP

[ding-swj]

Body:
Create a small CLI recorder that can run a command and export an AgentScope trace file.

Example:
agentscope record -- npm test

Scope:

• Record command, start time, duration, exit code, stdout/stderr
• Generate a .trace.json file compatible with docs/trace-schema.json
• Keep the first version simple and local-only

Acceptance criteria:

• Running a command creates a valid trace JSON file
• The generated trace can be imported into the web UI
• npm run lint and npm run build pass