feat: Generation Page AI workflows + AI/Vector modules + exam session fixes

Generation Page (complete rebuild):
- Full production-parity exam generation wizard with 4 IELTS modules
- Reading: AI passage gen, 5 exercise types (MCQ, Fill, Write, T/F, Match)
- Listening: 4 section types, AI context gen, TTS audio gen (ElevenLabs)
- Writing: Task 1/2, AI instruction gen, word limits, marks
- Speaking: 3 parts, AI script gen, avatar video gen (7 avatars)
- Per-module config: timer, CEFR difficulty, access, approval, rubrics
- Exam submission workflow (draft/published)

Exam Structures:
- New encoach.exam.structure model + CRUD controller
- ExamStructuresPage wired to real API

AI Module (encoach_ai):
- OpenAI service, ElevenLabs TTS, AWS Polly, ELAI avatars
- AI settings model with Odoo config parameters
- 7 generation endpoints (passage, exercises, instructions, scripts, context)

Vector Module (encoach_vector):
- pgvector integration for RAG-based content search
- Embedding service with sentence-transformers

Exam Session Fixes:
- Fixed ExamSession.tsx field mapping (question_type→type, exam_title→title)
- Fixed submit payload to include attempt_id and answers
- Fixed normalizeType to handle null/undefined

Tested: 12/12 API tests passed, browser-verified with real OpenAI calls
Made-with: Cursor

src/components/ai/AiGradingAssistant.tsx

@@ -26,9 +26,8 @@ export default function AiGradingAssistant({
   const gradeMutation = useMutation({
     mutationFn: () =>
       analyticsService.getGradingSuggestion({
-        submission_id: submissionId,
-        text: submissionText,
-        ...(rubricId !== undefined ? { rubric_id: rubricId } : {}),
+        submission_text: submissionText,
+        skill: "writing",
       }),
     onError: (err: Error) => {
       toast({
@@ -45,7 +44,7 @@ export default function AiGradingAssistant({
   }, [submissionId, submissionText, rubricId]);
 
   const data = gradeMutation.data;
-  const marks = data ? Math.round(data.overall_score) : 0;
+  const marks = data ? Math.round(data.overall_band * 100 / 9) : 0;
   const feedbackBlock = data
     ? [
         data.feedback,