Generalize provider usage bucket groups

[iam-brain]

Summary

This PR adds a generic provider-owned bucket-group mechanism for extra live rate-limit sections and uses Codex OAuth Spark data as the first implementation.

The goal is to support provider-specific rate-limit buckets without widening the existing primary / secondary / tertiary model or adding more one-off snapshot fields.

Why this approach:

• It keeps the current primary / secondary / tertiary model intact, so existing menu bar ranking, pace logic, and provider behavior stay stable.
• It gives providers one reusable path for extra rate-limit sections through snapshot data instead of more provider-specific fields.
• It keeps provider-specific detection in the provider mapping layer while making presentation data-driven in shared renderers.
• It matches the repo’s preference for typed snapshot data over provider-specific UI branching or metadata flags.

What changed:

• Added UsageBucketGroupSnapshot and UsageBucketSnapshot to UsageSnapshot as usageBucketGroups.
• Mapped Codex OAuth additional_rate_limits into a generic bucket group:
  • group id: codex.spark
  • group title: GPT-5.3-Codex-Spark
  • bucket ids: codex.spark.session, codex.spark.weekly
• Updated the menu descriptor, menu card, status menu, and CLI renderer to display extra bucket groups generically.
• Added regression coverage for OAuth decoding, snapshot round-tripping, CLI rendering, menu rendering, and status menu ordering/separators.

What intentionally did not change:

• No scanner, pricing, or history code.
• No changes to the existing primary / secondary / tertiary semantics.
• No new provider metadata booleans or provider-specific rendering branches for extra buckets.

Verification

• swift test
• pnpm check
• ./Scripts/compile_and_run.sh

[chatgpt-codex-connector]

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