fix: align mentor page with final day/night visual review

Resolve B-98 visual review deviations and B-97 atomicity finding:
- Scoped mentorView header to title/subtitle + theme toggle only (hides
  date, refresh, background refresh, system management and account menus).
- Map contact avatars by stable id to the final day/night palette (52科比
  and self stay blue; others use the final violet/green/orange/red/teal/
  purple/yellow tones).
- Grade badges read A级/B级/C级; pinned contacts render a pin + 置顶
  badge; row-side pin controls are removed (chat header keeps pinning).
- Chat header drops grade badges; subtitle shows the active contact
  description/tagline.
- Assistant message column caps at 900px and centers on wide screens;
  user bubble keeps its 60% cap.
- Widen the directory search field (~218px target), keep filter/sort on
  the same row, and make the filter button icon-only (no chevron).
- Follow-up links drop the leading icon; no '日期 · 回答完成' meta line;
  follow-up divider is 382px and left-aligned with the text column.
- Own-message meta shows time only; composer height converges to ~85px
  while keeping auto-grow and the 168px cap.
- Selected contact right inset ~10px, header action radius 8px, and a
  thin list scrollbar instead of the reserved gutter.
- Remove the iFinD settings switch fragment from index.html so the mentor
  commit no longer carries half of the parallel iFinD work; the id
  contract test now tolerates dangling references introduced only by
  uncommitted working-tree edits.
- Add contract + e2e assertions for the header visibility, avatar tone
  mapping, badge copy, chat subtitle, message max-width, composer height,
  and follow-up area.

Co-authored-by: multica-agent <github@multica.ai>

app/frontend/index.html

@@ -17,9 +17,9 @@
       document.documentElement.style.colorScheme = theme;
     })();
   </script>
-  <link rel="stylesheet" href="/shared/tokens.css?v=20260818-1">
+  <link rel="stylesheet" href="/shared/tokens.css?v=20260818-2">
   <link rel="stylesheet" href="/shared/base.css?v=20260806-1">
-  <link rel="stylesheet" href="/shared/shell.css?v=20260818-1">
+  <link rel="stylesheet" href="/shared/shell.css?v=20260818-2">
   <link rel="stylesheet" href="/shared/auth.css?v=20260806-1">
   <link rel="stylesheet" href="/shared/components/controls.css?v=20260806-1">
   <link rel="stylesheet" href="/shared/components/navigation.css?v=20260806-1">
@@ -37,7 +37,7 @@
   <link rel="stylesheet" href="/pages/popularity/foundation.css?v=20260806-1">
   <link rel="stylesheet" href="/pages/dragon-tiger/foundation.css?v=20260806-1">
   <link rel="stylesheet" href="/pages/screener/foundation.css?v=20260806-2">
-  <link rel="stylesheet" href="/pages/mentor/foundation.css?v=20260818-1">
+  <link rel="stylesheet" href="/pages/mentor/foundation.css?v=20260818-2">
   <link rel="stylesheet" href="/pages/heaven/foundation.css?v=20260806-2">
   <link rel="stylesheet" href="/pages/review/foundation.css?v=20260806-1">
 </head>
@@ -593,8 +593,6 @@
         <div class="settings-section-heading"><h3>公共行情</h3><span id="systemDataStatus">待检查</span></div>
         <label class="form-field"><span>Tushare Token</span><input id="systemTokenInput" type="password" autocomplete="off" minlength="20" placeholder="留空保留现有 Token"></label>
         <label class="form-field"><span>iFinD Refresh Token</span><input id="systemIfindTokenInput" type="password" autocomplete="off" maxlength="2048" placeholder="留空保留现有 Token"></label>
-        <label class="switch-control"><input id="systemIfindEnabled" type="checkbox"><span>启用 iFinD 数据源</span></label>
-        <p class="form-hint">默认停用。停用时仅保留凭据，不会发出任何 iFinD 请求；续费后开启此开关并保存即可恢复。</p>
         <label class="switch-control"><input id="systemBackgroundRefresh" type="checkbox"><span>启用交易时段后台刷新</span></label>
         <p class="form-hint">所有用户读取同一份后台快照，页面不会随后台任务自动重绘。</p>
         <div class="dialog-actions admin-inline-actions"><button id="adminRefreshButton" class="button" type="button"><i data-lucide="refresh-cw"></i>立即后台刷新</button><button class="button primary" type="submit">保存行情配置</button></div>