fix(codex): meter background and subagent activity

[qmarco-be]

Summary

• keep Codex snapshot collection running while Codex is backgrounded or the widget is hidden
• cache the latest Session snapshot and keep the live Codex face on the desktop instead of falling back to an idle global face
• resolve active subagent rollout metadata back to the root session and include the full Session tree
• add a persisted Focused / All active setting to the native widget
• aggregate all recently token-active root Sessions in All active mode, with per-Session model, rate, Context, and child-Agent counts
• de-duplicate Session trees by session_id so subagent rollouts are never counted as separate roots

Why

The native overlay previously requested codex-snapshot only while a Codex window was frontmost. When Codex moved to the background, collection stopped and the always-visible panel switched to a slow machine-wide snapshot that appeared idle. The single recency-selected Session could also mask concurrent work in another task, including GPT-6 tasks and their subagents.

Focused mode preserves the small existing active-candidate behavior. All active mode reads the same local rollout telemetry and sums every recently active Session tree. Context remains per root because unrelated context-window percentages cannot be meaningfully added.

Validation

• npm run check
• focused regression suite: 34/34 passed
• full suite: 195/197 passed; the two failures are existing timezone-sensitive usage-history fixture expectations under Asia/Shanghai and are outside this change
• live local probe: correctly reported two simultaneous root Sessions (gpt-5.6-sol and background gpt-6-astra) and attributed 28 child Agents to the GPT-6 root once
• built, ad-hoc signed, installed, and signature-verified /Applications/Token Widget.app

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