feat: add paid subscriber metrics and live dashboard subscriber stats (v0.3.12)

[cucoleadan]

Summary of Changes

• Integrated live publication subscriber stats endpoints (/api/v1/publication/stats/subscribers\ and /api/v1/publish-dashboard/summary) with fallback to email delivery stats.
• Normalized \ otal_subscribers, \paid_subscribers, \ree_subscribers, \�pp_subscribers, and tier breakdowns (comp, gift, trial, founding, lifetime, pledges).
• Added \get_paid_subscribers\ / \getPaidSubscribers\ tool and client method.
• Updated \get_subscriber_summary\ and \get_subscriber_stats\ tools to accurately return the active subscriber count instead of defaulting to \