fix(desktop): surface agent rename relay profile sync failure as a warning toast

[ayobamiseun]

Fixes #1822

Problem

Renaming an agent via the agent settings dialog performs a local save (always succeeds) and a best-effort relay kind:0 republish (can fail: network blip, auth expiry, relay unreachable). On sync failure the dialog console.warn'd the error and closed as a clean success — the user had no signal that the relay still holds the old name, which breaks @mention resolution and shows the stale name in other agents' From: lines (discovered via #1743).

Fix

Surface profileSyncError as a toast.warning in AgentInstanceEditDialog, matching the treatment the create and persona-save paths already give the same field (useManagedAgentActions.ts, UserProfilePanelPersonaSubmit.ts). The save is not blocked — the local rename is valid and persists, per the issue's guidance.

The toast points at the retry path that actually works: restarting the agent. Re-saving the same name does not retry — update_managed_agent computes name_changed against the already-updated record, so a second identical save skips the sync — but start_managed_agent fires reconcile_agent_profile, which queries the relay's kind:0 and republishes when the display name diverges.

Scope notes:

• EditRespondToDialog (the third caller of the update mutation) never changes the name, and the Rust side only sets profile_sync_error when the name changed — so no change needed there.
• The alternative fix in the issue (retry-with-backoff in sync_managed_agent_profile) is not taken here; reconcile_agent_profile on agent start already provides self-healing, and this change makes that path discoverable at the moment of failure.

Testing

• just desktop-check — biome + file-size + px-text + pubkey-truncation guards clean.
• just desktop-test — 3331 passed, 0 failed.
• The handler branch is a straight conditional on the mutation result; the repo's .test.mjs convention covers extracted pure logic, and there is no extracted logic here to unit-test (consistent with the equivalent toast branches on the create/persona paths).