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/jobs/src/payloads/notifications.ts

@@ -0,0 +1,49 @@
+import * as z from 'zod';
+
+/**
+ * Org branding carried through to the `quizAssigned` email. Mirrors
+ * `@cio/email`'s `ZEmailBranding`; defined inline so this lean queue package
+ * doesn't take a dependency on the email package. Re-validated against the
+ * email template schema at send time.
+ */
+const ZNotifyBranding = z
+  .object({
+    orgName: z.string().optional(),
+    logoUrl: z.string().url().optional(),
+    themeColor: z
+      .string()
+      .regex(/^#([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/)
+      .optional()
+  })
+  .optional();
+
+/**
+ * Payload for a `notifications:notify-course-exercise` job. Fired when a
+ * teacher clicks "Notify students" on an exercise — the worker fans out one
+ * `quizAssigned` email per course member with a deep link to take the quiz.
+ */
+export const ZNotifyCourseExercisePayload = z.object({
+  courseId: z.string().min(1),
+  exerciseTitle: z.string().min(1),
+  courseName: z.string().min(1),
+  orgName: z.string().min(1),
+  fromName: z.string().min(1),
+  quizUrl: z.string().min(1),
+  branding: ZNotifyBranding
+});
+export type TNotifyCourseExercisePayload = z.infer<typeof ZNotifyCourseExercisePayload>;
+
+/** Periodic scan that emails 24h/1h reminders for upcoming live sessions. No payload. */
+export const ZSessionReminderScanPayload = z.object({}).default({});
+export type TSessionReminderScanPayload = z.infer<typeof ZSessionReminderScanPayload>;
+
+/**
+ * Payload for a `notifications:notify-course-session-update` job. Fired when a
+ * teacher changes a live lesson's time/link — emails every member an updated
+ * calendar invite (same UID, higher SEQUENCE).
+ */
+export const ZNotifyCourseSessionUpdatePayload = z.object({
+  courseId: z.string().min(1),
+  lessonId: z.string().min(1)
+});
+export type TNotifyCourseSessionUpdatePayload = z.infer<typeof ZNotifyCourseSessionUpdatePayload>;