feat(reply-quality): 👎 keeps a snapshot of the turn; admin 对话质量记录

A 👎 now saves, server side, the rated turn plus the context window the
model read for it (reconstructed from the stored session with the same
consultationHistoryWindow the consult route uses), model and run facts.
👍 is only counted. Switching to 👍 or clearing deletes the snapshot.
Bodies are blanked after 90 days; the row cascades on session delete
and on account deletion.

- Optional 不满意原因 panel under the answer after a 👎 (five reasons,
  200-char note, "会把这一轮对话发给我们排查").
- Admin 对话质量记录: 👍/👎 stats by day and model, list without text,
  audited snapshot open, 处理状态 + note (support.quality.read/write).
- Privacy draft: what a 👎 keeps, why, 90 days, deletion.
- Migration 20260930050000 is add-only; set_reply_rating() replaced with
  the same signature.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4f2nya58RoRu4yEmJgRGE

frontend/src/components/admin/admin-app.tsx

@@ -7,6 +7,7 @@ import {
   ControlOutlined,
   CreditCardOutlined,
   DatabaseOutlined,
+  DislikeOutlined,
   ExperimentOutlined,
   GiftOutlined,
   MessageOutlined,
@@ -114,6 +115,7 @@ export function AdminApp({ children }: { children: ReactNode }) {
               { name: "usage", list: "/admin/usage", meta: { label: "用量与成本", icon: <ExperimentOutlined /> } },
               { name: "rectification-telemetry", list: "/admin/rectification-telemetry", meta: { label: "校正统计", icon: <BarChartOutlined /> } },
               { name: "feedback", list: "/admin/feedback", meta: { label: "反馈与投诉", icon: <MessageOutlined /> } },
+              { name: "reply-quality", list: "/admin/reply-quality", meta: { label: "对话质量记录", icon: <DislikeOutlined /> } },
               { name: "models", list: "/admin/models", meta: { label: "模型配置", icon: <ApiOutlined /> } },
               { name: "feature-pricing", list: "/admin/feature-pricing", meta: { label: "功能定价", icon: <CreditCardOutlined /> } },
               { name: "pricing-simulator", list: "/admin/pricing-simulator", meta: { label: "定价测算", icon: <ExperimentOutlined /> } },