fix(timeline): fix blank room timeline when app returns from background

[Just-Insane]

Description

When the app returns from background, retryImmediately() triggers a fresh sliding sync response. If the server includes initial: true for the currently open room, the SDK emits RoomEvent.TimelineReset, replacing the live timeline with a new empty one. eventsLength drops to 0 but isReady stays true, leaving the message list visually blank for ~500 ms until events re-arrive from the server.

Changes

RoomTimeline.tsx

• Added a useLayoutEffect that detects eventsLength dropping to 0 while the timeline is already visible (isReady === true). It immediately sets isReady = false and resets hasInitialScrolledRef, re-arming the existing initial-scroll logic. Uses useLayoutEffect so the transition happens before the browser paints — the blank frame is never shown.

• Expanded showLoadingPlaceholders, vListItemCount, and the container opacity to include the !isReady case, so skeleton placeholders are shown immediately during the reload rather than leaving an invisible list.

Before / After

Before	After
Room goes blank for ~500 ms on foreground return	Skeleton placeholders appear instantly, then content fades in

Fixes #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

AI disclosure:

Fully AI generated (explain what all the generated code does in moderate detail).

The useLayoutEffect guard and the three !isReady condition expansions were fully AI generated. The effect fires synchronously before paint when eventsLength drops to 0 on an already-visible timeline, hides content and resets the initial-scroll flag. The existing 80 ms scroll timer then re-runs once events refill and calls setIsReady(true). The showLoadingPlaceholders / vListItemCount changes ensure VList renders 3 placeholder skeleton rows (matching the existing pagination-loading behaviour) while events are absent.