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/pages.config.js

@@ -47,7 +47,7 @@
     ["heaven", "/pages/heaven/page.html?v=20260803-1", ["heavenView"]],
     ["ladder", "/pages/ladder/page.html?v=20260803-1", ["ladderView"]],
     ["screener", "/pages/screener/page.html?v=20260804-1", ["screenerView", "screenerTrackingView"]],
-    ["mentor", "/pages/mentor/page.html?v=20260818-1", ["mentorView"]],
+    ["mentor", "/pages/mentor/page.html?v=20260818-2", ["mentorView"]],
     ["rotation", "/pages/rotation/page.html?v=20260803-1", ["rotationView"]],
     ["auction", "/pages/auction/page.html?v=20260803-1", ["auctionView"]],
     ["themes", "/pages/themes/page.html?v=20260803-1", ["themeLibraryView"]],
@@ -81,7 +81,7 @@
     "/pages/popularity/page.js?v=20260729-1",
     "/pages/dragon-tiger/page.js?v=20260806-1",
     "/pages/screener/page.js?v=20260806-1",
-    "/pages/mentor/page.js?v=20260818-1",
+    "/pages/mentor/page.js?v=20260818-2",
     "/pages/heaven/page.js?v=20260729-1",
     "/pages/review/page.js?v=20260729-1",
     "/shared/state.js?v=20260729-1",