fix(desktop): clean up managed agents when channel is deleted

[wesbillman]

Summary

When a channel is deleted, managed agents that were created for that channel (via the "Add agents" dialog) are now automatically cleaned up. Previously, these agents would be orphaned — still running and visible in the Agents panel — after the channel was deleted.

What changed

New file: desktop/src/features/channels/cleanupChannelAgents.ts

• Extracted helper that handles the cleanup logic
• Fetches channel members, managed agents, and relay agents in parallel
• Cross-references to find managed agents that are members of the channel
• Only deletes agents that are NOT members of any other channel (multi-channel safe)
• Uses Promise.allSettled for best-effort cleanup — individual failures don't block others

Modified: desktop/src/features/channels/hooks.ts

• useDeleteChannelMutation now calls cleanupChannelAgents() before deleting the channel
• Cleanup is wrapped in try/catch — if it fails, channel deletion still proceeds
• onSettled invalidates managed-agents and relay-agents queries so the UI refreshes

Design decisions

• Delete, not just stop: Since each agent is a duplicate created specifically for the channel, deleting it (stop process + remove config) is the right call
• Multi-channel safe: Agents that are members of other channels are preserved
• Best-effort: Cleanup failures are logged but never prevent channel deletion
• No backend changes: This is a pure UI fix — the relay/database are untouched

Testing

Manually tested by the reporter — confirmed agents are cleaned up after channel deletion.