Folds the existing project-level Slack/Discord webhooks into the notification system as routable channels - so a "post status changed" event lands in the right Slack channel based on per-user prefs, not just blasted to every channel for every event. Keeps the existing webhook URL fields on projects (zero migration risk) but adds per-user override: a member can connect their personal Slack workspace via Slack OAuth and choose to receive their notifications as DMs from a Hollahoop bot instead of (or in addition to) the project channel firehose.

Same shape for Discord (per-user OAuth + DM via the Hollahoop bot user). Falls back gracefully: when a user has no personal connection, they only see the channel-wide messages the org already configured. Schema: user_chat_connections (user_id, provider enum slack|discord, external_user_id, access_token, refresh_token, scope, created_at).

Out of scope: rebuilding the existing channel webhooks - those keep working as the org-level default.