Implement opt-in accountability and motivation features (peer/teacher check-ins, badges)

[coreysreid]

Summary:
Design and add an accountability system that allows users to:

• Opt-in to share their progress with peers or mentors via a code (e.g., "accountability partner" or "teacher check-in").
• Set and track daily/weekly goals (e.g., "100 cards a day").
• See peer/teacher view dashboards of progress and study stats (read-only; no admin override rights).
• Earn visible badges/awards for milestones/consistency (future extension).

Acceptance Criteria:

• Account sharing is always user-initiated/consensual, removes admin overreach.
• No one (not even teachers) can edit or administer another person's study data—just observe.
• Accountability data is kept separate from content creation/management.
• Plan/account for eventual badge/award system.

Rationale:

• Boosts motivation through social accountability while preserving self-driven philosophy.
• Enables teachers to coach adaptively without having admin rights over student accounts.
• Lays the foundation for gamified engagement.

Label: enhancement