Non-owner members never get agents in desktop/web mention autocomplete (kind-10100 records present and correct; Agent Directory renders them)

## Summary

Community members (non-owners) never see agents in the desktop/web mention autocomplete, even when kind-10100 agent-profile records exist on the relay with a `respond_to_allowlist` that includes the viewer. The **Agent Directory** on the Agents tab renders the same records correctly for the same viewer — only the composer autocomplete fails. Mobile is unaffected (it resolves mentions from channel members).

## Environment

- Hosted community (`*.communities.buzz.xyz`), remote agents per `docs/remote-agents.md` (systemd launcher, `buzz-acp` harness, NIP-OA auth tags)
- Reproduced on desktop 0.4.26 AND a current 0.5.x client (two different users/machines)
- Agents are members of the channels in question, with published kind-0 profiles (carrying valid NIP-OA `auth` tags) and kind-10100 records

## What we established

1. **The desktop app (0.4.26 at least) never publishes kind-10100 records** for provider-backed agents. A relay dump (`REQ kinds:[10100]`, NIP-42-authed member) returned zero events in a community with 6 active agents. Owner-side autocomplete works anyway via the local managed-agents registry — so the gap is invisible to the agent owner and hits only other members.
2. We published complete records ourselves (agent-signed over WS; schema per `nostr_convert.rs::agents_from_events`): `name`, `display_name`, `agent_type`, `status`, `channels`, `channel_ids`, `respond_to: "allowlist"`, `respond_to_allowlist` (including the test viewer), `channel_add_policy`. Accepted (`OK true`), and readable by a non-owner member over an authenticated REQ.
3. After that: Agent Directory lists the agents for the non-owner viewer ✓ — but the composer `@` autocomplete still offers only humans ✗. Per source (`useMentions.ts` + `agentAutocompleteEligibility.ts`), the allowlist branch of `relayAgentIsSharedWithUser` should admit the viewer and `shouldHideAgentFromMentions` should show invocable agents, so the data and the visible code both say this should work.

## Expected

A member on an agent's `respond_to_allowlist` (or `anyone` with a shared channel) should get that agent in mention autocomplete — matching the directory, and matching what the harness would actually accept.

## Impact

Remote/provider-backed agents (the architecture `docs/remote-agents.md` formalizes) are effectively single-player on desktop/web: only their owner can mention them. Teams fall back to mobile or to replying inside agent threads.

Happy to provide the record dumps, event IDs, or run diagnostics against our community.