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/send.ts

@@ -94,7 +94,8 @@ export async function sendEmail<TEmailId extends EmailId>(
       template,
       fields: validatedFields,
       from: config.from ?? template.from,
-      replyTo: config.replyTo ?? template.replyTo
+      replyTo: config.replyTo ?? template.replyTo,
+      ics: config.ics
     });
   } catch (error) {
     if (error instanceof ZodError) {