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/jobs/package.json

@@ -14,12 +14,14 @@
     "dev:media": "tsx watch src/workers/media.ts",
     "dev:media-transcribe": "tsx watch src/workers/media-transcribe.ts",
     "dev:emails": "tsx watch src/workers/emails.ts",
+    "dev:notifications": "tsx watch src/workers/notifications.ts",
     "dev:maintenance": "tsx watch src/workers/maintenance.ts",
     "dev:agent-course-generation": "tsx watch src/workers/agent-course-generation.ts",
     "start": "node dist/index.js",
     "start:media": "node dist/workers/media.js",
     "start:media-transcribe": "node dist/workers/media-transcribe.js",
     "start:emails": "node dist/workers/emails.js",
+    "start:notifications": "node dist/workers/notifications.js",
     "start:maintenance": "node dist/workers/maintenance.js",
     "start:agent-course-generation": "node dist/workers/agent-course-generation.js",
     "lint": "eslint . --ext .ts",