fix(web): 账户弹窗移出 inert；校正快照失败不再静默（BUG-968/969）

账户弹窗与入门付费墙 portal 到 document.body，SidebarInset 的 inert 不再罩住弹窗。
GET 校正快照每个非 200 打 JSON warn；客户端失败显示「这一问还没读到」和重新读取。
下一题是可渲染选择题时，确定性回复正文带题干，挂卡后去重。

frontend/DESIGN.md

@@ -532,6 +532,7 @@ page. Three parts now, in reading order:
 
 ### Settings dialog
 
+- **Placement:** the overlay and the onboarding paywall portal to `document.body`. `SidebarInset` stays `inert` while a dialog is open (the BUG-744~746 focus contract); the dialog itself must not sit inside that subtree (BUG-968). Closing still uses the existing overlay click, the header button, and the window-level Escape listener.
 - **Structure:** one fixed chrome for four panes — 个人资料, 星盘资料, 账户与点数, 通用设置. Left nav is 176px and does not scroll; the title bar stays put; only the right-hand content pane scrolls. Logout stays a separate 400px confirmation.
 - **Width / height:** desktop `width: min(100vw - 32px, 880px)`, with `height: min(84vh, 640px)` as the base and `min(84dvh, 640px)` applied inside `@supports (height: 1dvh)`. All four panes share one class (`.settings-modal`), so switching panes cannot change the frame. At ≤767px the dialog is full-screen with four equal tabs along the top.
 - **Pane menu states:** default is transparent with secondary ink; hover is a 55% wash of `--color-canvas-muted` keeping secondary ink; current is the solid muted surface with primary ink. No accent bar, and no weight change — hierarchy here comes from ink rank and surface, matching “Hierarchy inside the nav comes from ink rank, not hue”. The sidebar's 2px `--sidebar-ring` on the active session is deliberately **not** changed to match; the two surfaces read differently on purpose until that is revisited.