feat(slack): enable assistant-agent tools via assistant:write scope

Add assistant:write, app_mentions:read, and im:history to the Slack bot
OAuth scopes so the Set Assistant Status / Title / Suggested Prompts tools
(assistant.threads.*) work with users' existing Slack credentials — no new
app or credentials required. Restore the action_assistant trigger capability
(scope assistant:write) in the manifest generator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpeT8J5yVCrrNQB9Hzm9uS

Author: TheodoreSpeaks

apps/sim/lib/oauth/oauth.ts

@@ -711,7 +711,9 @@ export const OAUTH_PROVIDERS: Record<string, OAuthProviderConfig> = {
           'groups:write',
           'chat:write',
           'chat:write.public',
-          // TODO: Add 'assistant:write' once Slack app review is approved
+          'assistant:write',
+          'app_mentions:read',
+          'im:history',
           'im:write',
           'im:read',
           'users:read',

apps/sim/triggers/slack/capabilities.ts

@@ -105,7 +105,16 @@ export const SLACK_CAPABILITIES: readonly SlackCapability[] = [
     scopes: ['channels:history', 'groups:history', 'im:history', 'mpim:history'],
     events: [],
   },
-  // TODO: Restore the 'action_assistant' capability (scope 'assistant:write') once Slack app review is approved
+  {
+    id: 'action_assistant',
+    label: 'Drive assistant threads',
+    description:
+      'Let the bot set the assistant status, title, and suggested prompts on assistant threads (assistant.threads.*).',
+    defaultChecked: true,
+    group: 'action',
+    scopes: ['assistant:write'],
+    events: [],
+  },
   {
     id: 'action_read_files',
     label: 'Read file attachments',