refactor(frontend): 优化 Gemini 配额显示，参考 Antigravity 样式

- 简化标签：将 "RPD Pro/Flash" 改为 "Pro/Flash"，避免文字截断
- 添加账号类型徽章（Free/Pro/Ultra），带颜色区分
- 添加帮助图标（?），悬停显示限流政策和官方文档链接
- 重构显示布局：账号类型 + 两行配额（Pro/Flash）
- 移除冗余的 AccountQuotaInfo 组件调用

backend/migrations/017_add_gemini_tier_id.sql

@@ -26,5 +26,10 @@ UPDATE accounts
 SET credentials = credentials - 'tier_id'
 WHERE platform = 'gemini'
   AND type = 'oauth'
-  AND credentials->>'oauth_type' = 'code_assist';
+  AND jsonb_typeof(credentials) = 'object'
+  AND credentials->>'tier_id' = 'LEGACY'
+  AND (
+    credentials->>'oauth_type' = 'code_assist'
+    OR (credentials->>'oauth_type' IS NULL AND credentials->>'project_id' IS NOT NULL)
+  );
 -- +goose StatementEnd