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/components/editor/utils.ts

@@ -148,7 +148,6 @@ export const resetEditor = (editor: Editor) => {
 };
 
 export const resetEditorHistory = (editor: Editor) => {
-  // eslint-disable-next-line no-param-reassign
   editor.history = {
     undos: [],
     redos: [],
@@ -228,7 +227,6 @@ export const getPointUntilChar = (
     reverse: options.reverse,
   });
 
-  // eslint-disable-next-line no-restricted-syntax
   for (const point of pointItr) {
     if (!Point.equals(point, cursorPoint) && prevPoint) {
       char = Editor.string(editor, { anchor: point, focus: prevPoint });