fix(sliding-sync): cache emoji packs, fix edit message rendering

[Just-Insane]

Summary

Three sliding-sync related fixes:

1. Cache emoji / image packs in localStorage

imagePackCache.ts — new localStorage cache for ImagePack instances, keyed by user/scope. All five hooks in useImagePacks.ts now seed from cache on cold-start and write through on change. Reduces reliance on sliding sync delivering custom emoji state before first render.

2. Prevent edit event leakage + align required_state

• reactionOrEditEvent now also detects edits via m.new_content presence as a fallback for when the sliding sync proxy strips m.relates_to — prevents stripped edit events from falling through and rendering as separate "Unsupported message" bubbles.
• required_state in slidingSync.ts extended with m.room.power_levels and cosmetics state events (m.room.cosmetics.*), which were previously missing from bundled subscriptions.

3. Re-render on non-live Replace events + guard empty getContent()

Two fixes for edited messages showing as "Broken/Unsupported message" until an unrelated live event triggered a re-render:

useRelationUpdate hook — listens for non-live RoomEvent.Timeline events with rel_type=m.replace. Sliding sync delivers bundled/historical edits as non-live events that are silently ignored by useLiveEventArrive; this hook triggers a shallow setTimeline update immediately when they arrive.

Empty getContent() guard — when the sliding sync proxy delivers a Replace event with m.relates_to intact but m.new_content absent, the SDK's makeReplaced() causes mEvent.getContent() to return {}. Passing {} to RenderMessageContent produces "Broken message". Fix: detect the empty result and fall back to mEvent.getOriginalContent(), which bypasses makeReplaced and returns the original unmodified content. msgType is now derived from the same resolved content object.