fix(ui): replace ungated invented CSS vars with folds tokens (native-cinny audit 1/N)

Audit of our delta vs Cinny v4.12.3 found invented CSS vars (--tc-*, --bg-*)
used outside Lotus-Terminal-gated code, which render unstyled/wrong on stock
themes. Batch 1:
- MemberVerificationBadge: --tc-positive/warning-normal -> color.Success/Warning.Main
- RoomInput (gif/location errors): --tc-danger-normal -> color.Critical.Main
- MsgTypeRenderers (location iframe): --bg-surface-border -> color.SurfaceVariant.ContainerLine
- MessageSearch (cached-room row): --bg-surface-variant -> color.SurfaceVariant.Container
- PrescreenControls (mic-denied): --tc-critical-high -> color.Critical.Main

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

src/app/features/message-search/MessageSearch.tsx

@@ -1,5 +1,17 @@
 import React, { RefObject, useCallback, useEffect, useMemo, useRef, useState } from 'react';
-import { Text, Box, Icon, Icons, config, Spinner, IconButton, Line, toRem, Button } from 'folds';
+import {
+  Text,
+  Box,
+  Icon,
+  Icons,
+  color,
+  config,
+  Spinner,
+  IconButton,
+  Line,
+  toRem,
+  Button,
+} from 'folds';
 import { useAtom, useAtomValue } from 'jotai';
 import { useVirtualizer } from '@tanstack/react-virtual';
 import { useInfiniteQuery } from '@tanstack/react-query';
@@ -112,7 +124,7 @@ function EncryptedRoomCachePanel({ roomIds, onLoaded }: EncryptedRoomCachePanelP
             gap="200"
             style={{
               padding: config.space.S200,
-              background: 'var(--bg-surface-variant)',
+              background: color.SurfaceVariant.Container,
               borderRadius: config.radii.R300,
             }}
           >