Add CLI client analytics and error event reporting

Context

The memU CLI should report acquisition-to-activation and client-side error events through the memu-service backend ingestion API. This must be best-effort and user-controllable.

Scope

Implement v1 CLI client event reporting.

Requirements

• Generate and persist a frontend-owned client_instance_id locally on first CLI use.
• Submit events to POST /api/memu/analytics/events once the backend issue is available.
• Include client_type=memu_cli, client_instance_id, CLI version, session id, agent platform, OS, deployment mode, install source, and memory mode where available.
• Track v1 activation events:
  • cli_install_started
  • cli_setup_completed
  • first_memory_committed
  • first_retrieve_succeeded
  • core_action_completed
• Track sanitized CLI errors using structured fields such as error_code, failure_stage, success, duration_ms, and recoverable.
• Do not report API keys, prompts, memory content, retrieve queries, file paths, plaintext identity, tokens, or full stack traces.
• Support opt-out, including MEMU_TELEMETRY=0.
• Telemetry failures must never fail the core CLI command.

Acceptance Criteria

• CLI has a stable local client_instance_id.
• Supported events are submitted best-effort to the backend endpoint.
• MEMU_TELEMETRY=0 disables submissions completely.
• Sensitive data is not included in telemetry payloads.

Priority: P2 Size: M Schedule: Now