Summary

• Adds a session_created telemetry event that fires when a new session is created
• Logs safe session config fields: agent, agent_mode, permission_mode, model, variant
• Does not include workdir or any sensitive paths
• Respects existing telemetry enabled/disabled flag (--no-telemetry)
• Sends asynchronously via spawned task to avoid blocking session creation

Test plan

• cargo check passes
• Verify event reaches telemetry endpoint with correct fields
• Verify no event is sent when --no-telemetry is set