setup: correct Slack member-ID card directions

Slack's profile button is in the bottom-left of the desktop sidebar (not
the top-right), and the "More" overflow icon next to "Copy member ID" is
the vertical kebab `⋮`, not the horizontal `⋯`. Match what users actually
see in Slack.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

setup/channels/slack.ts

@@ -308,9 +308,9 @@ async function collectSlackUserId(): Promise<string> {
     [
       "To get your Slack member ID:",
       '',
-      '  1. In Slack, click your profile picture (top right)',
+      '  1. In Slack, click your profile picture (bottom left)',
       '  2. Click "Profile"',
-      '  3. Click the three dots (⋯) → "Copy member ID"',
+      '  3. Click the three dots (⋮) → "Copy member ID"',
     ].join('\n'),
     'Find your Slack user ID',
   );