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/room/RoomTimeline.tsx

@@ -1,4 +1,3 @@
-/* eslint-disable react/destructuring-assignment */
 import React, {
   Dispatch,
   MouseEventHandler,
@@ -557,6 +556,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
       base += len;
       return seg;
     });
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- eventsLength detects in-place timeline mutations
   }, [timeline.linkedTimelines, eventsLength]);
   const liveTimelineLinked =
     timeline.linkedTimelines[timeline.linkedTimelines.length - 1] === getLiveTimeline(room);