fix(ui): settings modal sizing regression + 17 more folds audit findings

Fix settings modal regression: Modal500 was wrapped in useModalStyle(560),
forcing maxWidth 560px and squishing the two-pane Settings layout (folds
size="500" is ~50rem). Restore desktop width to the folds recipe while
keeping mobile fullscreen.

N-series fixes:
- N13 ScheduledMessagesTray header: <Box as="button"> -> folds <Button>
- N28 composer char counter: drop undefined --tc-surface-low + opacity,
  use priority="300" and config.space token
- N31 collapsible "Read more" toggle: padded <Button> -> flush inline-button
  pattern matching (edited) link
- N41 UserPrivateNotes "Saving..." now shows a folds <Spinner>
- N43 Night Light slider: add accentColor; label opacity -> priority
- N44 mention-highlight Reset: bare <button> -> folds <Button> (drops
  undefined --border-interactive-normal); Boot button kept (TDS-only)
- N45 SelectTheme trigger variant -> Secondary to match SettingsSelect
- N49 RoomInsights StatTile emoji -> folds <Icon> (Photo/VideoCamera/
  Headphone/File)
- N54/N57 PiP overlay badges + fullscreen button: token discipline
  (config.radii/space, folds Text); dark scrim kept for video legibility
- N60 knock badge: match Pinned Messages pattern (no wrapper div, toRem
  insets, no hardcoded size overrides)
- N62 unverified-device banner: 3px left-accent -> standard border via
  color.Warning.ContainerLine; drop opacity hacks
- N65 Edit History: real "Load more" pagination (accumulate next_batch,
  de-dupe by id, re-sort by ts) replacing passive text
- N66 search date fields: raw <input type="date"> -> folds <Input>
- N67 SeasonalEffect z-index 9999 -> 9997 (below Night Light + modals)
- N73 Pending Requests header uses css.MembersGroupLabel
- N74 remove raw em-sized emoji <span> in RoomNavItem name
- N85/N86 RemindMeDialog: <Box role="dialog"> -> folds <Dialog>; preset
  MenuItems -> Buttons (fixes invalid menuitem-in-dialog ARIA)

Document deliberate WON'T FIX rationale for N9, N51, N61, N71, N75, N77.

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

src/app/components/Modal500.tsx

@@ -2,14 +2,14 @@ import React, { ReactNode } from 'react';
 import FocusTrap from 'focus-trap-react';
 import { Modal, Overlay, OverlayBackdrop, OverlayCenter } from 'folds';
 import { stopPropagation } from '../utils/keyboard';
-import { useModalStyle } from '../hooks/useModalStyle';
+import { ScreenSize, useScreenSizeContext } from '../hooks/useScreenSize';
 
 type Modal500Props = {
   requestClose: () => void;
   children: ReactNode;
 };
 export function Modal500({ requestClose, children }: Modal500Props) {
-  const modalStyle = useModalStyle(560);
+  const isMobile = useScreenSizeContext() === ScreenSize.Mobile;
   return (
     <Overlay open backdrop={<OverlayBackdrop />}>
       <OverlayCenter>
@@ -21,7 +21,25 @@ export function Modal500({ requestClose, children }: Modal500Props) {
             escapeDeactivates: stopPropagation,
           }}
         >
-          <Modal size="500" variant="Background" style={modalStyle}>
+          <Modal
+            size="500"
+            variant="Background"
+            // On mobile expand to fill the viewport. On desktop fall back to the
+            // folds `size="500"` width (~50rem) — overriding maxWidth here would
+            // squish the two-pane settings layout.
+            style={
+              isMobile
+                ? {
+                    width: '100%',
+                    height: '100%',
+                    maxWidth: '100%',
+                    maxHeight: '100%',
+                    borderRadius: 0,
+                    overflow: 'hidden auto',
+                  }
+                : undefined
+            }
+          >
             {children}
           </Modal>
         </FocusTrap>