One page rule for both ends; the help overlay shows how to page

improvise-5xbq: resolve::page_rows is now the one home of the page-scroll
rule; the TUI's Move calls it instead of repeating visible_rows * 3 / 4.
A lockstep case pages (PgDn/PgUp, Ctrl-d/Ctrl-u) on a non-square window,
8 rows by 3 columns, and pins the TUI's landing rows as well as comparing
host and client, since one home moves both ends together. Both faults
the ticket injected (page_rows = window_rows / 2; paging by window_cols)
now fail at the first PgDn, before and after the move to one home.

improvise-1c5m: the help overlay draws the mode's own hint (hint_line,
the string #hint carries) in a sticky footer, so a narrow window whose
app bar wraps under #help still says how to page. Playwright case at
600px, red at base, and red again with the footer made non-sticky.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

web/app.js

@@ -348,7 +348,13 @@ function paintHelp(model) {
     }
   }
 
-  el.help.replaceChildren(tabs, body);
+  // The mode's own hint again, as the TUI popup's footer: once the app bar
+  // wraps, the overlay covers `#hint` (improvise-1c5m).
+  const footer = document.createElement("p");
+  footer.className = "help-footer";
+  footer.textContent = model.hint;
+
+  el.help.replaceChildren(tabs, body, footer);
 }
 
 /** The page bar: which item each fixed category is fixed to. Without it a