feat: live class sessions, CE workflow, and docs (#683)

Adds live-class session scheduling on lessons (join link, date/time,
timezone) with automatic 24h and 1h reminder emails plus a calendar
invite (.ics), a time-change notification with an updated invite, a
teacher-authored welcome email and session invite on enrollment, and a
"Notify students" quiz nudge.

LMS gets an upcoming live-sessions card and Join buttons, plus a
reusable live-session card component (3 states) in @cio/ui with a
Storybook story. The sidebar content tree now reflects sequential
progression locking like the content list, and the course-completion
confetti regression is fixed.

Org-based emails no longer reference ClassroomIO by name. Docs add
live-class, welcome-email, and course-progression guides, expand the
certificates guide (design, signatures, corrected labels), move
plan-required callouts to the top, flatten how-to-guides to the docs
root with redirects, and add screenshots. Includes an add-docs-image
skill.

apps/api/src/services/course/payment-request.ts

@@ -2,7 +2,7 @@ import { AppError, ErrorCodes } from '@api/utils/errors';
 
 import { getCourseTeachers } from '@cio/db/queries/course/people';
 import { getCourseWithOrgData } from '@cio/db/queries/course';
-import { buildEmailFromName } from '@cio/email';
+import { buildEmailFromName, buildEmailBranding } from '@cio/email';
 import { enqueueTransactionalEmail } from '@api/services/jobs';
 import { trackServerEvent, SERVER_EVENTS } from '@cio/analytics';
 
@@ -27,6 +27,11 @@ export async function createPaymentRequest(data: PaymentRequestData) {
 
     const courseName = course.courseTitle || '';
     const orgName = course.orgName || 'ClassroomIO';
+    const branding = buildEmailBranding({
+      name: course.orgName,
+      avatarUrl: course.orgAvatarUrl,
+      theme: course.orgTheme
+    });
     const groupId = course.groupId;
 
     if (!groupId) {
@@ -48,7 +53,8 @@ export async function createPaymentRequest(data: PaymentRequestData) {
         fields: {
           courseName,
           studentEmail: data.studentEmail,
-          studentFullname: data.studentFullname
+          studentFullname: data.studentFullname,
+          branding
         },
         from: buildEmailFromName('ClassroomIO'),
         idempotencyKey: `payment-request:teacher:${data.courseId}:${data.studentEmail}`
@@ -64,7 +70,8 @@ export async function createPaymentRequest(data: PaymentRequestData) {
           courseName,
           teacherEmail,
           studentFullname: data.studentFullname,
-          orgName
+          orgName,
+          branding
         },
         from: buildEmailFromName(`${orgName} - ClassroomIO`),
         replyTo: teacherEmail,