Fixed MAC Starter setup guide

Property	Value
description	Clarified MAC Starter base-variant setup guidance and variant customization hand-off notes.
version	0.73.0
type	Fix
related	MAC Docs, MAC Starter, MAC Starter Setup

• Clarified that the setup guide applies to base starter variants used to create variant-specific builds.
• Documented that Mihai creates the apm, uc, and mls variants while other variants are customized and maintained by their owners.
• Added the recommended lowercase first-name-plus-last-name account username convention.
• Updated setup workflow language for Mihai account access, permalink saving, license keys, and variant-specific customization.
• Removed broad customization wording that referenced integrations and analytics in the base setup checklist.
• Removed the old post-import and variant hand-off sections from the setup page.