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

backend/custom_addons/encoach_ai/models/__init__.py

@@ -0,0 +1,2 @@
+from . import ai_settings
+from . import ai_log

backend/custom_addons/encoach_ai/models/ai_log.py

@@ -0,0 +1,35 @@
+from odoo import fields, models
+
+
+class EncoachAILog(models.Model):
+    _name = "encoach.ai.log"
+    _description = "AI Service Call Log"
+    _order = "create_date desc"
+
+    service = fields.Selection(
+        [
+            ("openai", "OpenAI"),
+            ("whisper", "Whisper"),
+            ("polly", "AWS Polly"),
+            ("elevenlabs", "ElevenLabs"),
+            ("gptzero", "GPTZero"),
+            ("elai", "ELAI"),
+            ("coach", "AI Coach"),
+        ],
+        required=True,
+        index=True,
+    )
+    action = fields.Char(index=True)
+    model_used = fields.Char()
+    prompt_tokens = fields.Integer(default=0)
+    completion_tokens = fields.Integer(default=0)
+    total_tokens = fields.Integer(default=0)
+    latency_ms = fields.Integer()
+    status = fields.Selection(
+        [("success", "Success"), ("error", "Error"), ("timeout", "Timeout")],
+        default="success",
+    )
+    error_message = fields.Text()
+    user_id = fields.Many2one("res.users", default=lambda self: self.env.uid)
+    input_preview = fields.Text()
+    output_preview = fields.Text()

backend/custom_addons/encoach_ai/models/ai_settings.py

@@ -0,0 +1,79 @@
+from odoo import api, fields, models
+
+
+class EncoachAISettings(models.TransientModel):
+    _inherit = "res.config.settings"
+
+    # ── OpenAI ──
+    ai_openai_api_key = fields.Char(
+        string="OpenAI API Key",
+        config_parameter="encoach_ai.openai_api_key",
+    )
+    ai_openai_model = fields.Selection(
+        [("gpt-4o", "GPT-4o"), ("gpt-4o-mini", "GPT-4o Mini"), ("gpt-3.5-turbo", "GPT-3.5 Turbo")],
+        string="OpenAI Model",
+        default="gpt-4o",
+        config_parameter="encoach_ai.openai_model",
+    )
+    ai_openai_fast_model = fields.Selection(
+        [("gpt-4o-mini", "GPT-4o Mini"), ("gpt-3.5-turbo", "GPT-3.5 Turbo")],
+        string="OpenAI Fast Model",
+        default="gpt-3.5-turbo",
+        config_parameter="encoach_ai.openai_fast_model",
+    )
+
+    # ── AWS Polly ──
+    ai_aws_access_key = fields.Char(
+        string="AWS Access Key ID",
+        config_parameter="encoach_ai.aws_access_key",
+    )
+    ai_aws_secret_key = fields.Char(
+        string="AWS Secret Access Key",
+        config_parameter="encoach_ai.aws_secret_key",
+    )
+    ai_aws_region = fields.Char(
+        string="AWS Region",
+        default="eu-west-1",
+        config_parameter="encoach_ai.aws_region",
+    )
+
+    # ── ElevenLabs ──
+    ai_elevenlabs_api_key = fields.Char(
+        string="ElevenLabs API Key",
+        config_parameter="encoach_ai.elevenlabs_api_key",
+    )
+    ai_elevenlabs_model = fields.Char(
+        string="ElevenLabs Model",
+        default="eleven_multilingual_v2",
+        config_parameter="encoach_ai.elevenlabs_model",
+    )
+    ai_tts_provider = fields.Selection(
+        [("polly", "AWS Polly"), ("elevenlabs", "ElevenLabs")],
+        string="TTS Provider",
+        default="polly",
+        config_parameter="encoach_ai.tts_provider",
+    )
+
+    # ── GPTZero ──
+    ai_gptzero_api_key = fields.Char(
+        string="GPTZero API Key",
+        config_parameter="encoach_ai.gptzero_api_key",
+    )
+
+    # ── ELAI ──
+    ai_elai_token = fields.Char(
+        string="ELAI Token",
+        config_parameter="encoach_ai.elai_token",
+    )
+
+    # ── Operational ──
+    ai_max_retries = fields.Integer(
+        string="Max Generation Retries",
+        default=3,
+        config_parameter="encoach_ai.max_retries",
+    )
+    ai_enabled = fields.Boolean(
+        string="AI Services Enabled",
+        default=True,
+        config_parameter="encoach_ai.enabled",
+    )