E2E: Fix sidebar unread indicators (@wip cluster A)

[mjkatgithub]

Planning

• Milestone: Phase 3
• Priority: P0
• Size: M
• Estimate: 2 SP
• Epic: Re-enable @wip chat E2E scenarios quarantined for green CI lane #134

Goal

Fix sidebar unread state so inactive channels show data-unread="true" when
another user posts, clear on open, survive reload, and aggregate mentions on
the space rail.

Scope

• Unread indicator for inactive channel
• Opening channel clears unread indicator
• Unread indicator survives reload
• Mention unread aggregates on the space rail
• Remove @wip when green

Branch

bug/e2e-wip-unread

Acceptance criteria

• All four cluster A scenarios pass without @wip.
• Green mention/unread scenarios still pass.

Test checklist

E2E

• Unread / mention scenarios in chat.feature

Unit (if composables change)

• npm run test:unit for unread helpers

Notes

Root cause: hasUnread relied on Matrix NotificationCountType.Total, which
stays zero for normal group messages under default push rules; mentions
(Highlight) already worked.

Fix: activity-based fallback in roomUnread.ts (getEventReadUpTo vs latest
foreign message, including encrypted via getLastLiveEvent); mute rooms skip
fallback; useRoomUnread passes userId, notification level, and refreshes on
sync/unread-notification events. E2E steps select Home + scoped sidebar locators
(unread + I open the seeded test room). @wip removed from four cluster A
scenarios.

Verified: 6/6 targeted unread E2E green; full lane 36/40 (all cluster A +
mention regression pass; 4 unrelated flakes incl. create-space rail).

Docs: N/A — logic in existing unread modules.