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/docs/content/docs/student-dashboard.mdx

@@ -43,7 +43,7 @@ Both show enrolled courses. My Learning adds clearer filtering for students mana
 **Explore** lists **published, active courses** in your organization that the student has **not** enrolled in yet. Each card links to the course landing page so they can read details and enroll (if enrollment is open).
 
 <Callout type="info" title="Explore is a catalog, not an enrollment gate">
-  A course can appear in Explore even when public self-enrollment is turned off. **Allow New Students** controls whether someone can join from the landing page, not whether the course is visible in Explore. To restrict who can join, see [How Course Enrollment Works](/docs/how-to-guides/course-enrollment).
+  A course can appear in Explore even when public self-enrollment is turned off. **Allow New Students** controls whether someone can join from the landing page, not whether the course is visible in Explore. To restrict who can join, see [How Course Enrollment Works](/docs/course-enrollment).
 </Callout>
 
 Explore is useful when you want students to discover optional or elective courses without assigning them manually.
@@ -82,7 +82,7 @@ If you added them from **People** but they have not signed in yet, they may show
 
 ## Related guides
 
-- [How Course Enrollment Works](/docs/how-to-guides/course-enrollment) — how students join courses and what settings control access
-- [How to Invite Students](/docs/how-to-guides/invite-students) — send enrollment links by email
+- [How Course Enrollment Works](/docs/course-enrollment) — how students join courses and what settings control access
+- [How to Invite Students](/docs/invite-students) — send enrollment links by email
 - [Programs](/docs/programs) — multi-course tracks and goals for admins
-- [Create a Course Landing Page](/docs/how-to-guides/course-landingpage) — what prospects see before enrolling
+- [Create a Course Landing Page](/docs/course-landingpage) — what prospects see before enrolling