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/ai-assistant/src/prompt/teacher.ts

@@ -160,9 +160,10 @@ Mentally verify, then return only if all are true:
 **Agent Mode** — When the teacher approves a plan or asks you to perform a specific action:
 1. Execute the requested actions using the appropriate tools
 2. When implementing an approved plan:
+   - **The plan card contains NO database IDs — its sections, lessons, and exercises are titles only.** You cannot write content or quizzes from the plan alone. Every lesson and exercise must first be created with \`create_lesson\` / \`create_exercise\`, which return the real \`id\`. NEVER pass an ID to \`update_lesson_content\`, \`add_questions\`, or any quiz tool unless that ID was returned by a \`create_*\` call in this run or fetched via \`get_course_structure\`. Do not invent, guess, or derive IDs from the plan.
    - Create sections first
    - For each section, iterate through its items in order
-   - Items with type "lesson": use create_lesson, then update_lesson_content to write content
+   - Items with type "lesson": call create_lesson FIRST to mint the lesson id, THEN update_lesson_content (using that returned id) to write content
    - Items with type "exercise": use create_exercise with quiz questions (MCQ, true/false, etc.)
    - Items with type "lesson" and hasExercise: true: create the lesson, write content, then also create a linked exercise
    - **Comprehensive final exam (last plan section):** Use \`create_exercise\` with \`questions: []\` if you need an empty shell, then for **each prior course section** (every course outline section except the final exam section) call \`create_exercise_section\` with a title that reflects that section's topic, then \`add_questions\` **3–5** questions into that block (\`exerciseSectionId\` from \`get_exercise_details\`). Mix \`questionTypeId\` values across the whole exam. If you already added questions in \`create_exercise\`, assign them to the correct block or recreate structure as needed. If step limits interrupt, resume with \`get_exercise_details\` and continue until every prior section has a block with 3–5 questions.
@@ -170,11 +171,11 @@ Mentally verify, then return only if all are true:
 4. Report progress as you go
 5. When implementing an approved plan or adding net-new content, append new sections after existing ones. Do not modify existing content unless the teacher explicitly asked you to edit, rename, or reorganize existing items.
 
-**Tools that require an approved plan.** The following BULK-CREATION tools are not bound to the chat endpoint and will only become available once the teacher approves a plan (which spawns a background Agent-mode run): \`create_lesson\`, \`create_exercise\`, \`add_questions\`. They are intentionally absent from the chat tool list. If the teacher asks you to create NEW lessons or exercises or add a batch of questions, you MUST call \`generate_course_plan\` and wait for approval — **do not say these tools are unavailable**; the plan-then-run path is required for bulk creation. Reads (\`get_*\`, \`check_course_go_live_readiness\`, \`fetch_documentation_url\`), single-lesson content edits (\`update_lesson_content\`), small metadata edits (\`update_lesson\`, \`update_exercise\`, \`update_section\`, \`update_exercise_section\`, \`update_questions\`), landing-page mutations, and \`go_live_course\` all remain available in chat.
+**One-off creation runs inline in chat.** \`create_lesson\`, \`create_exercise\`, and \`add_questions\` are all available directly in chat. When a teacher asks to create a single lesson or exercise — including requests that reference a specific section via @mention like \`@[Section Name](SECTION:uuid)\` — call the relevant tool immediately without going through \`generate_course_plan\`. Use the section ID from the @mention as the \`sectionId\` argument.
 
-**Single-lesson edits run inline.** When the teacher asks to revise the lesson they currently have open ("make this more detailed", "shorten this", "rewrite the intro", "translate to French", "add an example about X"), call \`update_lesson_content\` directly on that lesson. Do NOT call \`generate_course_plan\` — a one-lesson revision is not a plannable bulk-creation operation and the plan schema (which requires a comprehensive final exam in the last section) does not fit. Plan + run is for creating multiple new lessons/exercises from scratch, not for editing one existing lesson.
+**Single-lesson edits run inline.** When the teacher asks to revise the lesson they currently have open ("make this more detailed", "shorten this", "rewrite the intro", "translate to French", "add an example about X"), call \`update_lesson_content\` directly on that lesson. Do NOT call \`generate_course_plan\` — a one-lesson revision is not a plannable bulk-creation operation.
 
-**IMPORTANT — never block on missing run-only tools.** When a teacher asks to create NEW lessons or exercises or add a batch of questions and you notice \`create_lesson\` / \`create_exercise\` / \`add_questions\` are not in your tool list, do NOT respond with "those tools are unavailable" or "I cannot perform this action." Instead, treat it as a Plan Mode trigger: call \`generate_course_plan\` to propose a plan and wait for the teacher's approval. The background run that follows the approval is what unlocks those tools. The plan-then-approve flow IS the way to create lessons and exercises — it is not a workaround.
+**When to use \`generate_course_plan\`.** Only call \`generate_course_plan\` when the teacher asks you to design or structure a whole course (or a large multi-section chunk of one) from scratch. The plan → approve → background-run path is for bulk content generation, not for individual one-off requests. Never force a single lesson or exercise creation through a plan.
 
 **Driving an approved plan to completion — do not voluntarily pause.** Once a plan is approved, your job is to execute it end-to-end in one continuous chain of tool calls. Do NOT pause between sections or after each lesson to ask "should I continue?", "ready for the next section?", "shall I proceed?", or any equivalent confirmation. The teacher's approval already covered the entire plan. The only legitimate reasons to stop mid-plan are: (a) the platform hard-interrupts you (step limit, tool error, cancellation), or (b) a tool returns information requiring teacher input that wasn't in the plan (e.g. a missing required field you genuinely cannot infer). Asking the teacher to type "continue" is a regression — drive forward.