Dead code cleanup — server actions + API routes

[Echolento]

Parent

#14

What to build

Remove orphaned server actions and API routes after feature removal. Clean up data-actions.ts and admin-actions.ts.

Remove from data-actions.ts

• Session-related: getTeacherDashboard (simplify), getTeacherSessions, createSession, completeSession, updateSessionDetails, deleteSession, getTeacherWeeklySessionCounts, checkSessionOverlap
• Session notes: createSessionNote, updateSessionNotes, getStudentLastSessionNotes
• Student progress: updateStudentProgress
• Admin: getAdminDashboard, getAllTeachers (admin variant), getAllStudents (admin variant), transferStudent, removeStudent, getAllOrganizations, createOrganization
• Unused payment analytics: getRevenueTrend, getPaymentHistory

Remove API routes

• /api/teachers/[id]/display if no longer needed

Remove

• admin-actions.ts entirely
• lib/invitation-actions.ts (if not already removed by student CRUD slice)

Keep

• Payment actions: getTeacherPayments, toggleStudentPayment, updateStudentMonthlyPrice, updateStudentPaymentDay
• Student actions: getTeacherStudents (simplified for new schema)
• Settings actions: updateTeacherSettings (simplified)
• Auth actions unchanged

End-to-end behavior: app compiles without errors, payment flow works, student management works, no references to removed server actions.

Acceptance criteria

• Session, session-note, progress server actions removed from data-actions.ts
• Admin and org server actions removed
• admin-actions.ts file deleted
• Unused payment analytics actions removed
• /api/teachers/[id]/display route removed if orphaned
• All imports cleaned up, no compilation errors
• Payments, students, settings, auth still work end-to-end

Blocked by

• Navigation strip + Dashboard simplification #16
• DB Migration — drop removed tables, alter students #18