feat: tag runtime API keys with request format

[SsuJojo]

Summary

• Add persisted format: "openai" metadata to runtime API keys and normalize legacy keys to OpenAI format.
• Carry format through API key add/import/export/list flows and submit the disabled OpenAI selector from the dashboard.
• Route dynamic API key adapters by request format so OpenAI-compatible format uses /chat/completions regardless of provider label.

摘要

• 为运行时 API keys 增加持久化的 format: "openai" 元数据，并将旧数据默认归一化为 OpenAI 格式。
• 在 API key 添加、导入、导出、列表流程中传递 format，并让 Dashboard 的禁用 OpenAI 格式选择器实际提交该值。
• 动态 API key adapter 按请求格式路由，OpenAI-compatible 格式会按 /chat/completions 请求，不再只依赖 provider 标签。

Test Plan

• npx vitest run tests/unit/auth/api-key-pool.test.ts tests/unit/routes/api-keys.test.ts tests/unit/proxy/adapter-factory.test.ts tests/unit/proxy/upstream-router-apikeys.test.ts web/src/components/ApiKeyManager.test.tsx
• npm run build:web
• npm run build
• git diff --check

[SsuJojo]

Superseded by #611. This branch has been reset to latest dev and no longer contains independent changes.