refactor(chat): remove QuotaDialog and related state/effects

Drop the QuotaDialog component invocation in chat-screen along with
its useState/useEffect wiring, and delete the component files. Update
JSDoc in chat-screen and routes to reflect the removed consumer.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/router/routes.ts

@@ -10,7 +10,7 @@
  *  - 动态深链通过 `ROUTE_BUILDERS` 函数生成，避免手拼字符串。
  *
  * 注意：proxy 路由跳转逻辑（2026-06-15 迁出），但本文件的**类型化常量**仍在
- * 被 9 个组件（auth-screen / chat-header / quota-dialog / DeepLinkPersist /
+ * 被 8 个组件（auth-screen / chat-header / DeepLinkPersist /
  * error / not-found / page / sidebar-screen / splash-screen）使用 —— **不能**整体注释。
  */