fix: select quota endpoint by credential

[victor0602]

Summary

• share credential-aware quota endpoint selection between the CLI and SDK
• route sk-api- API keys to /account/query_balance
• keep OAuth and Token Plan credentials on /v1/token_plan/remains
• expose the accurate SDK response union with public type guards
• document both quota response shapes and cover options, config-file, and OAuth credentials

Validation

• bun test test/sdk/quota.test.ts
• bun run typecheck
• bun run lint
• bun test (452 passed)

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