feat(sliding-sync): rewrite MSC4186 sliding sync to match Element Web approach

[Just-Insane]

Rewrites the sliding sync implementation to more closely match how Element Web handles MSC4186 simplified sliding sync. The classic sync path (startClassicSync) is not modified.

Sliding sync improvements (slidingSync.ts, initMatrix.ts)

• Room list sorted by notification level, then recency, then name (matching Element Web ordering)
• include_old_rooms added so tombstoned rooms pass predecessor state to their replacements
• Active-room custom subscription: the focused room receives timeline_limit=50; all other rooms use the default list subscription
• SlidingSyncManager.subscribeToRoom() / unsubscribeFromRoom() API for per-room subscription lifecycle
• getSlidingSyncManager() exported from initMatrix
• useSlidingSyncActiveRoom hook + SlidingSyncActiveRoomSubscriber component to wire the active room into the sliding sync subscription

Presence extension (slidingSync.ts)

• Implements a custom MSC4186 ExtensionPresence and registers it with the SlidingSync object
• Without this, the SDK's SlidingSyncSdk only auto-registers ExtensionToDevice and ExtensionAccountData, so extensions.presence.events payloads from the server were silently discarded — components using useUserPresence would always show stale/default presence
• The extension maps raw events through client.getEventMapper(), calls user.setPresenceEvent() to update User state, and emits ClientEvent.Event — matching the classic sync presence path exactly
• SlidingSyncManager.setPresenceEnabled() exposes an enable/disable toggle (consumed by the presence toggle in feat(presence): presence status setting #108)

Timeline reliability (RoomTimeline.tsx, ClientNonUIFeatures.tsx)

• Always reinitialise the timeline room on TimelineRefresh events (previously guarded by a stale liveTimeline reference check)
• Fixes a silent hang where the room timeline stops updating after a sliding sync reconnect

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Note: This branch currently contains a few unrelated commits (Docker build fix, notification delivery bugs, in-app bug report) that were included before the branch was scoped. These will be cleaned up / rebased out.