fix: ESLint errors, stale disable comments, bundle splitting

- RoomTimeline.tsx: add eslint-disable comment for intentional eventsLength
  dep on timelineSegments useMemo (needed to detect in-place timeline mutations)
- Remove ~47 stale eslint-disable-next-line comments across 28 files for rules
  that are now off in the flat config (no-param-reassign, jsx-a11y/media-has-caption,
  react/no-array-index-key, etc); run prettier to reformat
- vite.config.js: move manualChunks from rollupOptions.output to
  rolldownOptions.output so Rolldown (Vite 8) actually applies it; main bundle
  drops from 3.5 MB to 814 kB gzip-248 kB, matrix-sdk gets its own 1.16 MB
  cacheable chunk

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/common-settings/permissions/PermissionGroups.tsx

@@ -1,4 +1,3 @@
-/* eslint-disable react/no-array-index-key */
 import React, { useCallback, useEffect, useMemo, useState } from 'react';
 import { Badge, Box, Button, Chip, config, Icon, Icons, Menu, Spinner, Text } from 'folds';
 import { produce } from 'immer';

src/app/features/common-settings/permissions/Powers.tsx

@@ -1,4 +1,3 @@
-/* eslint-disable react/no-array-index-key */
 import React, { useState, MouseEventHandler, ReactNode } from 'react';
 import FocusTrap from 'focus-trap-react';
 import {