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

custom_addons/encoach_ai/__manifest__.py

@@ -0,0 +1,27 @@
+{
+    "name": "EnCoach AI Services",
+    "version": "19.0.1.0.0",
+    "category": "Education",
+    "summary": "Central AI service layer — OpenAI, Whisper, Polly, ElevenLabs, GPTZero, ELAI",
+    "description": """
+        Provides a unified AI service layer for the EnCoach platform.
+        - OpenAI GPT-4o / GPT-3.5-turbo (chat, JSON generation, grading)
+        - OpenAI Whisper (speech-to-text)
+        - AWS Polly (text-to-speech)
+        - ElevenLabs (text-to-speech, multilingual)
+        - GPTZero (AI content detection)
+        - ELAI (avatar video generation)
+        - AI Coaching assistant
+        - AI Search, Insights, Report Narrative
+    """,
+    "author": "EnCoach",
+    "depends": ["base", "encoach_core"],
+    "data": [
+        "security/ir.model.access.csv",
+        "views/ai_settings_views.xml",
+        "data/ai_defaults.xml",
+    ],
+    "installable": True,
+    "application": True,
+    "license": "LGPL-3",
+}