Refresh the conversation list while it is open

[AndyScherzinger]

Stacked on #6745, which is stacked on #6744. Review those first — their commits appear here until they merge.

With the list open, a message sent from another device only shows up when a push arrives or the user leaves and comes back. This adds the 30-second refresh timer iOS has, which matters most for the people who have no working push at all — no Play Services, no UnifiedPush distributor — for whom this becomes the only freshness mechanism the list has.

What it does

• A loop bound to the resumed lifecycle, so it cannot run behind the screen or outlive it. It waits before the first sync rather than after: onResume already fetches, and syncing on entry would fetch twice on every resume.
• Ticks are dropped while a sync is already in flight, so the loop can never queue behind itself, and while a search is open, so the list is not swapped out from under what the user is reading.
• Every tick is a delta sync. Without #6744 this would be a full room list every 30 seconds.

What a reviewer should push back on

• Two guards, not four. Being offline is already handled one layer down, where the sync returns without a request; battery saver already stops the expensive half, the message catch-up. Adding either here would only duplicate a check that exists.
• User status dots refresh every 5 minutes, not every 30 seconds. Delta syncs drop includeStatus, because with it the server returns every one-to-one room regardless of modifiedSince and most of the saving disappears. iOS keeps status fresher here; this trades that for the request volume.
• Accessibility: the tick reuses the existing silent sync path and introduces no animation and no focus change. Worth a TalkBack pass with focus parked mid-list.

Not in this PR

• A full refresh on delete / disinvite signaling messages, which would let the five-minute rule relax.

🚧 TODO

• TalkBack pass: focus parked mid-list across several ticks
• Manual: list open on device A, message from device B, appears within ~30 s

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI