Mobile mention autocomplete includes archived agent identities

## Summary

An archived duplicate agent that is no longer in the channel still appears in Buzz Mobile mention autocomplete on Android. Buzz Desktop correctly hides the archived identity.

## Environment

- Buzz Mobile: Android
- Paired desktop: Buzz Desktop 0.5.2 on Debian
- Agent: duplicate Kimi identity with the Codex avatar

## Steps to reproduce

1. Archive a duplicate managed agent identity.
2. Confirm that the archived identity is no longer a member of the channel.
3. Open the same channel in Buzz Mobile on Android.
4. Type @ followed by the agent name.
5. Observe both the active agent and the archived duplicate in autocomplete.

## Expected

Archived identities are excluded from mention autocomplete.

## Actual

The archived identity remains selectable in Mobile. Desktop filters it correctly.

## Notes

This appears to affect Mobile candidate assembly across channel members, the relay agent directory, or global profile search. Archiving should hide the identity without requiring deletion of its public profile.

Related: #2973

Reproduce the issue in Buzz Mobile on Android, then trace mention autocomplete candidate assembly across channel members, the relay agent directory, and global profile search; compare the filtering that Desktop already applies. Done means the archived duplicate is absent from Mobile autocomplete while the active agent remains selectable.

Written by the indexing model from the issue text.