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/student/StudentGrades.tsx

@@ -29,7 +29,7 @@ export default function StudentGrades() {
         <p className="text-muted-foreground">Track your academic performance.</p>
       </div>
 
-      <AiReportNarrative narrative={`Your average grade is ${avgGrade}%. Your strongest area is essay writing with consistent scores above 80%. Focus on improving speaking scores — your last mock test scored 72%, which is below your average. AI recommends practicing with the IELTS Speaking Masterclass materials.`} />
+      <AiReportNarrative report_type="grades" data={{ avgGrade, highest, count: gradeRecords.length }} />
 
       <div className="grid grid-cols-1 sm:grid-cols-3 gap-4">
         <Card><CardContent className="pt-6 text-center"><p className="text-sm text-muted-foreground">Average</p><p className="text-3xl font-bold text-primary">{avgGrade}%</p></CardContent></Card>