feat(providers): add CodeBuddy CN credit usage provider

[dong5945]

Summary

Adds a CodeBuddy CN provider so Win-CodexBar can show subscription credit remaining / used totals for Tencent CodeBuddy (codebuddy.cn).

What it tracks

• Account credit packages via POST https://www.codebuddy.cn/billing/meter/get-user-resource
• Summed CapacitySize / CapacityUsed / CapacityRemain across packages
• Optional earliest package expire time as reset

Auth sources (priority)

1. Manual Cookie header (Settings / token accounts)
2. %USERPROFILE%\.codebuddy\cb_cookie.txt (shared with statusline helpers)
3. Browser cookies for codebuddy.cn
4. Auto fallback: ~/.codebuddy/cb_credits.json normalized cache

Notes

• Uses a Chrome UA without Edg/ (EdgeOne WAF rejects Edge UAs on this path)
• Package codes can be overridden with CB_PACKAGE_CODES when an account returns empty Accounts
• Default-disabled in the provider catalog

Test plan

• cargo test -p codexbar --lib providers::codebuddy
• Enable CodeBuddy in Settings → paste Cookie from plans-usage Network tab → refresh
• Confirm remaining/total credits match https://www.codebuddy.cn/profile/plans-usage

Scope

CN CodeBuddy only (codebuddy.cn). International codebuddy.ai can be a follow-up.

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[Finesssee]

Thanks for the PR, I will review it ASAP.