fix(ui): folds primitives for RouteError + PiP fullscreen button (native-cinny audit 5/N)

- RouteError: raw <div>/<h2>/<p>/<button> (sans-serif, raw px) -> folds
  Box/Text/Button with config tokens.
- CallEmbedProvider PiP fullscreen control: raw <button> with ⊡/⛶ glyphs ->
  folds IconButton reusing the exported FullscreenIcon/ExitFullscreenIcon SVGs
  from Controls (consistent with the main fullscreen button). The intentional
  dark over-video scrim is kept.

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

src/app/pages/RouteError.tsx

@@ -1,5 +1,6 @@
 import React from 'react';
 import { useRouteError, isRouteErrorResponse } from 'react-router-dom';
+import { Box, Button, config, Text, toRem } from 'folds';
 
 export function RouteError() {
   const error = useRouteError();
@@ -11,33 +12,22 @@ export function RouteError() {
       : 'An unexpected error occurred.';
 
   return (
-    <div
-      style={{
-        display: 'flex',
-        flexDirection: 'column',
-        alignItems: 'center',
-        justifyContent: 'center',
-        height: '100dvh',
-        gap: '16px',
-        padding: '32px',
-        fontFamily: 'sans-serif',
-      }}
+    <Box
+      direction="Column"
+      alignItems="Center"
+      justifyContent="Center"
+      gap="400"
+      style={{ height: '100dvh', padding: config.space.S700 }}
     >
-      <h2 style={{ margin: 0, fontSize: '1.25rem' }}>Something went wrong</h2>
-      <p style={{ margin: 0, opacity: 0.7, textAlign: 'center' }}>{message}</p>
-      <button
-        type="button"
-        onClick={() => window.location.reload()}
-        style={{
-          padding: '8px 20px',
-          borderRadius: '8px',
-          border: 'none',
-          cursor: 'pointer',
-          fontWeight: 600,
-        }}
-      >
-        Reload
-      </button>
-    </div>
+      <Text size="H3">Something went wrong</Text>
+      <Text size="T300" priority="300" style={{ textAlign: 'center', maxWidth: toRem(400) }}>
+        {message}
+      </Text>
+      <Button variant="Primary" onClick={() => window.location.reload()}>
+        <Text as="span" size="B400">
+          Reload
+        </Text>
+      </Button>
+    </Box>
   );
 }