Background-tasks 'report running' setting now defaults to on

What

• The helper that decides whether background task / pending-notification status gets reported now reads the CLAUDE_CODE_BG_TASKS_REPORT_RUNNING env var directly and treats it as on unless it is explicitly set to false, replacing a previous implementation tied to focus-request settling.
• The tengu_tool_cpu_by_phase telemetry event's bg_tasks_report_running field now comes from that same normalized helper, instead of logging the raw (and possibly undefined) env var value.

Why Background task status reporting now works by default without needing the env var set explicitly, and the telemetry that records this setting is now accurate instead of reflecting an unset raw value.