Expose the per-model weekly rate limit in the statusline JSON

/usage shows three meters — session, week (all models), and week (Fable). The statusline JSON exposes only rate_limits.five_hour and rate_limits.seven_day, so the Fable weekly bucket can't be surfaced in a custom statusline.

Verified on v2.1.222 by capturing statusline payloads from Opus sessions, and from Fable sessions both before and after Fable usage registered:

| session | rate_limits keys |
| --- | --- |
| Opus 5 (8 captures) | five_hour, seven_day |
| Fable 5, no usage yet | five_hour, seven_day |
| Fable 5, usage registered | five_hour, seven_day |

The key set never changes, and the Fable percentage (94% at the time, per /usage) appears at no path in any payload. So it isn't model-scoped or usage-gated — it just isn't passed through. /usage renders it even while the session is on Opus.

Request: include the per-model weekly bucket in rate_limits. Gating rendering on the field's presence would keep it Fable-only automatically, with no extra config needed.