When user sends a DM to the Discord bot, the session's deliveryContext.to is incorrectly set to a server channel ID (channel:1476087708626587699) instead of the user's DM.

Steps to reproduce:

1. Configure Discord with allowlist for a user
2. User DMs the bot
3. Check sessions.json - deliveryContext.to shows "channel:<server_channel_id>" instead of "user:<user_id>"
4. Agent replies go to the server channel, not the DM

Expected: deliveryContext.to should be "user:<user_id>" for DM sessions
Actual: deliveryContext.to is "channel:<server_channel_id>"

Impact: User cannot receive agent replies in their DM - replies go to a server channel instead.

Workaround: Use message tool with explicit target to send to user DM.