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

frontend/src/pages/admin/AiEnglishQuality.tsx

@@ -113,7 +113,7 @@ export default function AiEnglishQuality() {
             <Button
               onClick={() =>
                 reject.mutate(
-                  { courseId, notes },
+                  { courseId, reason: notes },
                   {
                     onSuccess: () => {
                       toast.success("Rejected; regeneration requested.");

frontend/src/pages/admin/AiIeltsValidation.tsx

@@ -38,13 +38,11 @@ export default function AiIeltsValidation() {
 
   const send = (approved: boolean) => {
     if (!preview) return;
-    const payload: Parameters<typeof submitReview.mutate>[0] = {
-      item_id: preview.id,
-      approved,
-      notes: approved ? undefined : notes,
-      checklist,
-    };
-    submitReview.mutate(payload, {
+    submitReview.mutate({
+      logId: preview.id,
+      action: approved ? "approve" : "reject",
+      examiner_notes: approved ? undefined : notes,
+    }, {
       onSuccess: () => {
         toast.success(approved ? "Approved." : "Rejected with notes.");
         setPreview(null);