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/dashboard/src/lib/features/settings/utils/store.ts

@@ -14,3 +14,17 @@ export const landingPageSettings: Writable<OrgLandingPageJson> = writable(create
  * no section is selected — the editor shows the section list.
  */
 export const landingPageEditorSelection: Writable<LandingSectionKey | null> = writable(null);
+
+type SettingsHeaderAction = {
+  label: string;
+  disabled: boolean;
+  loading: boolean;
+  onClick: null | (() => void | Promise<void>);
+};
+
+export const settingsHeaderAction: Writable<SettingsHeaderAction> = writable({
+  label: 'Save',
+  disabled: true,
+  loading: false,
+  onClick: null
+});