[Feature Request] Expose per-model usage breakdown in statusline JSON and /usage endpoint

Bug Description
-Title: Expose per-model (Fable) usage in statusline JSON / /usage

Body:
The Claude Code statusline JSON schema currently exposes only account-level rate_limits.five_hour and rate_limits.seven_day usage
percentages, with no per-model breakdown. Now that Fable 5 (claude-fable-5) is a distinct model alongside Opus/Sonnet/Haiku, it would be
useful to see Fable-specific usage separately (e.g. rate_limits.by_model.fable.used_percentage), both in /usage output and in the scriptable
statusline stdin JSON, so custom statuslines can surface it.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.198
• Feedback ID: 09bc2626-ca06-4b9f-82fc-7bb145a96f88

Errors

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