feat(admin): student credential management, CSV import UI, remote classroom control center

- StudentsView: credential status in the roster table, a create-student form
  (email/login-ID/cohort), convert/reset-password/revoke-sessions controls per student, a
  bulk CSV import form. Every one-time activation/reset link is surfaced exactly once, never
  re-fetchable.
- ClassroomView: cohort picker -> schedule/list classes -> a live dashboard (participants with
  presence/Lab-status/current-work, help queue with acknowledge/resolve, current-activity
  setter, announcement poster, start/end/cancel, Prepare Labs). Polls the dashboard endpoint
  rather than a second push channel.
- AdminPortal: new Classroom nav entry. CohortsView's existing quick-add-student call updated
  for createStudent's new object-argument signature.

frontend/src/admin/api.js

@@ -16,7 +16,9 @@ function getCookie(name) {
 async function json(res) {
   if (!res.ok) {
     const body = await res.json().catch(() => ({}))
-    throw new Error(body.message || body.error || `Request failed (${res.status})`)
+    const err = new Error(body.message || body.error || `Request failed (${res.status})`)
+    if (body.row_errors) err.row_errors = body.row_errors // Phase 5A §29 — CSV import row-level errors
+    throw err
   }
   return res.json()
 }
@@ -49,8 +51,14 @@ export const adminApi = {
   dashboard: () => get('/api/admin/dashboard'),
 
   students: () => get('/api/admin/students'),
-  createStudent: (display_name, cohort_id) => post('/api/admin/students', { display_name, cohort_id }),
+  createStudent: (fields) => post('/api/admin/students', fields),
   updateStudent: (id, fields) => patch(`/api/admin/students/${id}`, fields),
+  // ── Phase 5A §4-7/§29: credential lifecycle + CSV import ────────────────────────────────
+  convertStudent: (id, fields) => post(`/api/admin/students/${id}/convert`, fields),
+  resetStudentPassword: (id) => post(`/api/admin/students/${id}/reset-password`),
+  revokeStudentSessions: (id) => post(`/api/admin/students/${id}/revoke-sessions`),
+  studentSessions: (id) => get(`/api/admin/students/${id}/sessions`),
+  importStudents: (csv) => post('/api/admin/students/import', { csv }),
   studentProgress: (id) => get(`/api/admin/students/${id}/progress`),
   studentAttempts: (id, page = 1) => get(`/api/admin/students/${id}/attempts?page=${page}`), // Phase 4.1 §16 — paginated, see pagination.js
   studentEnvironment: (id) => get(`/api/admin/students/${id}/environment`),
@@ -95,4 +103,17 @@ export const adminApi = {
   assignAssessment: (id, cohort_id) => post(`/api/admin/assessments/${id}/assign`, { cohort_id }),
   assessmentSessions: (id, page = 1) => get(`/api/admin/assessments/${id}/sessions?page=${page}`), // Phase 4.1 §16 — paginated, see pagination.js
   cancelAssessmentSession: (sessionId) => post(`/api/admin/assessment-sessions/${sessionId}/cancel`),
+
+  // ── Phase 5A §14/§21: remote classroom control center ───────────────────────────────────
+  classrooms: (cohortId) => get(`/api/admin/cohorts/${cohortId}/classroom-sessions`),
+  createClassroom: (cohortId, fields) => post(`/api/admin/cohorts/${cohortId}/classroom-sessions`, fields),
+  classroomDashboard: (id) => get(`/api/admin/classroom-sessions/${id}`),
+  startClassroom: (id) => post(`/api/admin/classroom-sessions/${id}/start`),
+  endClassroom: (id) => post(`/api/admin/classroom-sessions/${id}/end`),
+  cancelClassroom: (id) => post(`/api/admin/classroom-sessions/${id}/cancel`),
+  prepareClassroomLabs: (id) => post(`/api/admin/classroom-sessions/${id}/prepare-labs`),
+  setClassroomActivity: (id, scenario_id) => post(`/api/admin/classroom-sessions/${id}/activity`, { scenario_id }),
+  postClassroomAnnouncement: (id, message) => post(`/api/admin/classroom-sessions/${id}/announcements`, { message }),
+  acknowledgeHelpRequest: (id) => post(`/api/admin/help-requests/${id}/acknowledge`),
+  resolveHelpRequest: (id, note) => post(`/api/admin/help-requests/${id}/resolve`, { note }),
 }