feat: migrate MiniMax accounting and support CN endpoint

[niheaven]

Summary

Migrates MiniMax Coding Plan (international) and MiniMax Coding Plan (CN) from the pre-structured-accounting envelope to the standard QuotaProviderResult shape, fixing the CN provider not rendering on /quota.

What was changed:

• Bucket selection: Old plan takes the minimax-m* row (coding usage counts); new plan takes the general row (percent only). The video row is dropped — video-generation quota, irrelevant to an OpenCode coding-plan user.
• Basis unit uniformity: For the old-plan minimax-m* row, the 3-fact basis now uses one count: "request" unit. Previously the CN entry used mixed units, which the framework rejected.
• New-plan general row is basis-less: current_interval_total_count = 0, percent only — percentRemaining is already conveyed at row level.
• Structured accounting: Each emitted entry carries AccountingMetadata (quota / remote_api / maintained / provider_reported) and semantic (metric.kind = "window", prominence = "primary"), matching the upstream Accounting Result Contract.
• Labels: Coding Plan → Token Plan.

Linked Issue

• Fixes [bug]: MiniMax Token Plan (CN) does not display quota #232

Output

New token plan account: API returns general + video; plugin keeps general, drops video.

/quota toast:

[MiniMax Token Plan] (CN)
Five-hour quota    2h  ████████████░░░░░░░░░░░  33% left
Weekly quota      10d  █████████░░░░░░░░░░░░░░░  46% left

Old token plan (coding plan) account: API returns minimax-m* (+ minimax-h* etc. for image/video); plugin keeps minimax-m* only.

/quota toast:

[MiniMax Token Plan] (CN)
Five-hour quota    1d  ████████████████████░░░  95% left
  Used: 70 / Limit: 4500
Weekly quota       2d  ███████████████░░░░░░░░░  59% left
  Used: 44895 / Limit: 45000

OpenCode Validation

• Current production released OpenCode version tested: 1.18.21

Quality Checklist

• I ran pnpm run typecheck
• I ran pnpm run build
• I ran pnpm test
• This change is focused and avoids unrelated behavior changes
• I updated or added tests when behavior changed
• I updated docs when user-facing workflow, command, or config behavior changed
• For provider changes, I followed Provider Changes, or this does not apply

[niheaven]

Hmm, not to migrate MiniMax to new accounting format?

btw, it IS MiniMax Token Plan in OpenCode now.