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.

packages/email/src/emails/student-course-completion.ts

@@ -2,6 +2,7 @@ import * as z from 'zod';
 
 import { defineEmail } from '../send';
 import { getDefaultTemplate } from '../templates';
+import { ZEmailBranding } from '../core/branding';
 
 export const studentCourseCompletionEmail = defineEmail({
   id: 'studentCourseCompletion',
@@ -11,7 +12,8 @@ export const studentCourseCompletionEmail = defineEmail({
     courseName: z.string().min(1),
     studentName: z.string().min(1),
     certificateUrl: z.string().url(),
-    customMessage: z.string().nullable().optional()
+    customMessage: z.string().nullable().optional(),
+    branding: ZEmailBranding
   }),
   render: (fields) => {
     const customBlock =
@@ -28,6 +30,6 @@ export const studentCourseCompletionEmail = defineEmail({
       <p>Cheers,<br/>${fields.orgName}</p>
     `;
 
-    return getDefaultTemplate(content);
+    return getDefaultTemplate(content, fields.branding);
   }
 });