refactor(ui): extract shared SettingsSelect; replace raw <select> (native-cinny audit 6/N)

Extracted the folds-native dropdown (Button+PopOut+Menu) from General.tsx into a
shared components/settings-select/SettingsSelect.tsx, and used it to replace raw
native <select> elements (which render OS-styled and broke under non-default
themes via colorScheme:'dark'):
- Profile "auto-clear after" select
- PushRuleEditor add-rule mode select (dropped the now-unused handleModeChange)

The form-tied timezone <select> in Profile is left for a follow-up (it's wired
to native form submission + a disabled state and needs more care).

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

src/app/features/settings/notifications/PushRuleEditor.tsx

@@ -1,6 +1,7 @@
 import React, { ChangeEventHandler, FormEventHandler, useCallback, useMemo, useState } from 'react';
 import { IPushRule, IPushRules, PushRuleKind } from 'matrix-js-sdk';
 import { Box, Text, Button, Input, config, IconButton, Icons, Icon, Spinner, Switch } from 'folds';
+import { SettingsSelect } from '../../../components/settings-select/SettingsSelect';
 import { useAccountData } from '../../../hooks/useAccountData';
 import { AccountDataEvent } from '../../../../types/matrix/accountData';
 import { SequenceCard } from '../../../components/sequence-card';
@@ -193,10 +194,6 @@ function AddRuleForm({ kind, placeholder, label }: AddRuleFormProps) {
     setRuleId(evt.currentTarget.value);
   };
 
-  const handleModeChange: ChangeEventHandler<HTMLSelectElement> = (evt) => {
-    setMode(evt.target.value as NotificationMode);
-  };
-
   return (
     <Box as="form" onSubmit={handleSubmit} direction="Column" gap="200">
       <Text size="T200" priority="300">
@@ -217,24 +214,12 @@ function AddRuleForm({ kind, placeholder, label }: AddRuleFormProps) {
           />
         </Box>
         <Box shrink="No">
-          <select
+          <SettingsSelect
             value={mode}
-            onChange={handleModeChange}
-            style={{
-              background: 'transparent',
-              border: '1px solid currentColor',
-              borderRadius: config.radii.R300,
-              padding: `${config.space.S100} ${config.space.S200}`,
-              color: 'inherit',
-              fontSize: 'inherit',
-            }}
-          >
-            {ADD_MODES.map((m) => (
-              <option key={m} value={m}>
-                {MODE_LABELS[m]}
-              </option>
-            ))}
-          </select>
+            options={ADD_MODES.map((m) => ({ value: m, label: MODE_LABELS[m] }))}
+            onChange={setMode}
+            aria-label="Notification mode"
+          />
         </Box>
         <Button
           size="400"