feat: add integrations

Signed-off-by: kjuulh <contact@kjuulh.io>

specs/features/006-notification-integrations.md

@@ -238,7 +238,7 @@ Notification rules:
 
 1. Admin clicks "Add Slack" → `POST /orgs/{org}/settings/integrations/slack` with CSRF
 2. Server generates OAuth state (CSRF + org), stores in session, redirects to:
-   `https://slack.com/oauth/v2/authorize?client_id=...&scope=incoming-webhook,chat:write&redirect_uri=...&state=...`
+   `https://slack.com/oauth/v2/authorize?client_id=...&scope=assistant:write,channels:join,chat:write,chat:write.public,im:history,im:read,im:write,incoming-webhook,links:read,links:write,reactions:write,users:read,users:read.email&redirect_uri=...&state=...`
 3. User authorizes in Slack
 4. Slack redirects to `GET /orgs/{org}/settings/integrations/slack/callback?code=...&state=...`
 5. Server validates state, exchanges code for access token via Slack API