feat: restore mentor page to final day/night spec

Rebuild the mentor workspace per the approved final design (day.png/night.png):
- mentorView gets a dedicated full-width immersive shell (independent 56px
  top bar with page title slot + theme mode text, hidden module-nav/market
  tape/overview/status bar) scoped to body[data-active-view=mentorView].
- Assistant messages become borderless body text with name/time above; only
  user messages use a blue bubble; keep loading/error/streaming caret states.
- 4 quick topics stay visible with history; composer restored to a framed
  ~94px card with bottom-left shortcut hint and bottom-right send button.
- Directory tools merged into one row (search + filter menu + sort); the
  filter menu still offers all/A/B/C; list selected state is an inset rounded
  fill; contact rows are borderless 75px items.
- Chat header always shows pin/note/profile/clear; pin reuses /api/mentors/
  preferences; theme toggle stays the single #themeToggle.
- Night tokens match the spec including the two distinct blues (#316FEF link,
  #5B8DEF quote/selected icon). Mobile (<768) stacks panels with no horizontal
  overflow; 1024+ follows the desktop spec.
- Update stale test baselines (300px sidebar, 94px composer, hint presence,
  night bubble color, centered disclaimer) and regenerate the architecture
  inventory.

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

app/frontend/shared/shell.js

@@ -60,6 +60,7 @@
       const page = registry.get(viewId);
       const navigationId = page?.navigation_alias || viewId;
       const marketView = page?.group === "market";
+      const previousActiveView = document.body.dataset.activeView;
       document.body.dataset.activeView = viewId;
       const mobileGroup = document.querySelector("#mobilePageGroup");
       const mobileTitle = document.querySelector("#mobilePageTitle");
@@ -69,6 +70,10 @@
           : page?.group === "personal" ? "复盘" : "工具";
       }
       if (mobileTitle) mobileTitle.textContent = page?.title || "小白复盘";
+      const pageTitle = document.querySelector("#currentPageTitle");
+      if (pageTitle) pageTitle.textContent = page?.title || "小白复盘";
+      const pageSubtitle = document.querySelector("#currentPageSubtitle");
+      if (pageSubtitle && previousActiveView !== viewId) pageSubtitle.textContent = "";
       document.querySelectorAll(".module-tab").forEach((button) => {
         button.classList.toggle("active", button.dataset.view === navigationId);
         button.classList.toggle(