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/call/PrescreenControls.tsx

@@ -1,5 +1,5 @@
 import React, { useCallback, useEffect, useState } from 'react';
-import { Box, Button, Icon, Icons, Spinner, Text } from 'folds';
+import { Box, Button, color, Icon, Icons, Spinner, Text } from 'folds';
 import { SequenceCard } from '../../components/sequence-card';
 import * as css from './styles.css';
 import { ChatButton, ControlDivider, MicrophoneButton, SoundButton, VideoButton } from './Controls';
@@ -78,10 +78,7 @@ export function PrescreenControls({ canJoin }: PrescreenControlsProps) {
       </Box>
       <Box grow="Yes" direction="Column" gap="200">
         {micDenied && (
-          <Text
-            size="T200"
-            style={{ color: 'var(--tc-critical-high, #e53e3e)', textAlign: 'center' }}
-          >
+          <Text size="T200" style={{ color: color.Critical.Main, textAlign: 'center' }}>
             Microphone access is blocked. Enable it in your browser settings to join.
           </Text>
         )}