Expose Fable weekly usage (seven_day_fable) in status line rate_limits

What

The status line command's stdin JSON exposes rate_limits with five_hour, seven_day, seven_day_opus, and seven_day_sonnet, but there is no key for the Fable weekly limit. Please add rate_limits.seven_day_fable, with the same shape as the existing entries (used_percentage, resets_at), so status line scripts can render a Fable weekly usage bar.

Why

/usage already shows a separate Current week (Fable) limit alongside Current week (all models), so the data exists client-side. A custom status line can already render the all-models weekly (seven_day) and the per-model Opus/Sonnet weeklies (seven_day_opus, seven_day_sonnet) — but not the Fable one. Users on Fable-heavy workflows have no way to surface their Fable weekly usage in the status line and must open /usage to see it.

Version

Claude Code 2.1.237 (macOS, arm64). Confirmed present in this build: rate_limits.five_hour, .seven_day, .seven_day_opus, .seven_day_sonnet. Absent: any Fable weekly key.

Proposed

Add rate_limits.seven_day_fable (shape: { used_percentage, resets_at }), consistent with the existing per-model weekly keys.