fix(desktop): Custom Window Chrome toggle breaks the timeline (P5-47)

Toggling custom chrome expanded the screen and sent the message feed
auto-scrolling into the past. Two causes:
- DesktopChrome used height:100vh while html/#root use 100dvh; in the Tauri
  webview 100vh can exceed the visible height after decorations are stripped,
  making the timeline's scroll container taller than the viewport → the virtual
  paginator runs away paginating backwards. Switched to 100dvh.
- Toggling live reflowed the whole app while the timeline was mounted. The
  setting now persists + reloads so the layout is rebuilt cleanly (description
  updated: "reloads to apply").

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LOTUS_TESTING.md

@@ -675,6 +675,8 @@ Run the axe DevTools extension (or Lighthouse → Accessibility) on a room view,
 
 ## Outstanding verification backlog
 
+**Custom Window Chrome (Beta) fix (2026-07):** on the desktop build, Settings → General → toggle **Custom Window Chrome** — it should reload and come up with the Lotus title bar and a normal, stable feed (no screen-expand / auto-scroll-into-the-past). Toggle back off → reloads to the native frame.
+
 _Ported from the retired `LOTUS_BUGS.md` (2026-07). Compact index of shipped-but-not-live-tested items; the detailed steps are in the lettered sections above._
 
 Implemented and gate-green; confirm each per `LOTUS_TESTING.md`, then delete the row.