docs: improve Slack setup guide with channel event subscriptions and scopes

The #1 support issue with Slack is 'bot works in DMs but not channels'.
This is almost always caused by missing event subscriptions (message.channels,
message.groups) or missing OAuth scopes (channels:history, groups:history).

Changes:
- slack.md: Move channels:history and groups:history from optional to required
  scopes. Move message.channels and message.groups to required events. Add new
  'How the Bot Responds' section explaining DM vs channel behavior. Add Step 8
  for inviting bot to channels. Expand troubleshooting table with specific
  'works in DMs not channels' entry. Add quick checklist for channel debugging.
- setup.py: Expand Slack setup wizard with all required scopes, event
  subscriptions, and a warning that without message.channels/message.groups
  the bot only works in DMs. Add link to full docs. Improve Member ID
  discovery instructions.
- config.py: Update SLACK_BOT_TOKEN and SLACK_APP_TOKEN descriptions to list
  required scopes and event subscriptions inline.

hermes_cli/setup.py

@@ -1572,10 +1572,22 @@ def setup_gateway(config: dict):
     
     if not existing_slack and prompt_yes_no("Set up Slack bot?", False):
         print_info("Steps to create a Slack app:")
-        print_info("   1. Go to https://api.slack.com/apps → Create New App")
-        print_info("   2. Enable Socket Mode: App Settings → Socket Mode → Enable")
-        print_info("   3. Bot Token: OAuth & Permissions → Install to Workspace")
-        print_info("   4. App Token: Basic Information → App-Level Tokens → Generate")
+        print_info("   1. Go to https://api.slack.com/apps → Create New App (from scratch)")
+        print_info("   2. Enable Socket Mode: Settings → Socket Mode → Enable")
+        print_info("      • Create an App-Level Token with 'connections:write' scope")
+        print_info("   3. Add Bot Token Scopes: Features → OAuth & Permissions")
+        print_info("      Required scopes: chat:write, app_mentions:read,")
+        print_info("      channels:history, channels:read, groups:history,")
+        print_info("      im:history, im:read, im:write, users:read, files:write")
+        print_info("   4. Subscribe to Events: Features → Event Subscriptions → Enable")
+        print_info("      Required events: message.im, message.channels,")
+        print_info("      message.groups, app_mention")
+        print_warning("   ⚠ Without message.channels/message.groups events,")
+        print_warning("     the bot will ONLY work in DMs, not channels!")
+        print_info("   5. Install to Workspace: Settings → Install App")
+        print_info("   6. After installing, invite the bot to channels: /invite @YourBot")
+        print()
+        print_info("   Full guide: https://hermes-agent.ai/docs/user-guide/messaging/slack")
         print()
         bot_token = prompt("Slack Bot Token (xoxb-...)", password=True)
         if bot_token:
@@ -1587,7 +1599,7 @@ def setup_gateway(config: dict):
             
             print()
             print_info("🔒 Security: Restrict who can use your bot")
-            print_info("   Find Slack user IDs in your profile or via the Slack API")
+            print_info("   To find a Member ID: click a user's name → View full profile → ⋮ → Copy member ID")
             print()
             allowed_users = prompt("Allowed user IDs (comma-separated, leave empty for open access)")
             if allowed_users: