Series enrollment and auto-advance

[evanyerburgh]

[Platform: App]

Part of #269

Context

The new Series feature. Today practitioners enroll in each plan individually; this sub-issue introduces series-level enrollment and auto-advance from one plan to the next.

Acceptance Criteria

• One Enroll action on a Series About page enrolls the practitioner in all plans in that series
• After completing the last day of a plan, the practitioner is automatically advanced to day 1 of the next plan in the series
• Series-level progress is visible on the Plan landing and Home enrolled card
• After completing the last plan, the series is marked complete and the series celebration fires
• Standalone plan enrollment continues to work as before

Flags

• ⚠️ Only sub-issue that requires meaningfully new client-side behavior — the others are UI refreshes

References

• Figma: https://www.figma.com/design/0TE5qdViUvrisFZfNqODpX/WeBuddhist-App?node-id=4014-13975
• API: https://api.webuddhist.com/docs