Web frontend: hide app title and row titles, regroup help sheet, drop Ctrl+d/u

- New SHOW_APP_TITLE switch (off): the mascot + title header goes, the status pill
  stays on a slim row of its own.
- SHOW_ROW_TITLES off; with only icons, the shelf icon moves into a column left of
  the tiles so an icon-only shelf is no taller than one without.
- Help sheet regrouped into sections in a compact two-column grid, and reachable
  from a small keyboard button (not on phones or the typing page).
- Ctrl+d/Ctrl+u half-page jumps removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/components/AppHeader.tsx

@@ -1,5 +1,7 @@
 import type { ReactNode } from "react";
 
+import { SHOW_APP_TITLE } from "../lib/theme";
+
 interface Props {
   title?: string;
   mascot?: string;
@@ -15,6 +17,25 @@ export function AppHeader({
   status,
   compact = false,
 }: Props) {
+  if (!SHOW_APP_TITLE) {
+    // Still clear the translucent standalone-mode status bar, and keep the status
+    // pill - it is the only place an offline connection shows on these screens.
+    return (
+      <div
+        style={{
+          display: "flex",
+          justifyContent: "center",
+          padding: status
+            ? `calc(${compact ? 8 : 10}px + env(safe-area-inset-top)) 16px 0`
+            : "env(safe-area-inset-top) 0 0",
+          flex: "none",
+        }}
+      >
+        {status}
+      </div>
+    );
+  }
+
   const mascotSize = compact ? 44 : 64;
   return (
     <div