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/components/ai/AiWritingHelper.tsx

@@ -22,8 +22,9 @@ export default function AiWritingHelper({ text, task_type = "ielts_writing" }: P
   const mutation = useMutation({
     mutationFn: (mode: NonNullable<Mode>) =>
       coachingService.writingHelp({
-        text: text.trim(),
-        task_type: `${task_type}:${mode}`,
+        task: task_type,
+        draft: text.trim(),
+        help_type: mode,
       }),
     onSuccess: () => setShowResult(true),
     onError: (err: Error) => {
@@ -84,20 +85,20 @@ export default function AiWritingHelper({ text, task_type = "ielts_writing" }: P
 
         {showResult && !loading && mutation.data && activeMode === "improve" && (
           <div className="space-y-3">
-            {mutation.data.feedback && (
+            {mutation.data.tips?.length > 0 && (
               <div className="rounded-lg border bg-muted/30 p-3">
                 <p className="text-xs font-semibold text-primary mb-1 flex items-center gap-1">
                   <Sparkles className="h-3 w-3" /> Feedback
                 </p>
-                <p className="text-sm text-muted-foreground">{mutation.data.feedback}</p>
+                <p className="text-sm text-muted-foreground">{mutation.data.tips.join(" ")}</p>
               </div>
             )}
-            {mutation.data.improved && (
+            {mutation.data.improved_text && (
               <div className="rounded-lg border bg-muted/30 p-3">
                 <p className="text-xs font-semibold text-primary mb-1 flex items-center gap-1">
                   <Sparkles className="h-3 w-3" /> Improved Version
                 </p>
-                <p className="text-sm">{mutation.data.improved}</p>
+                <p className="text-sm">{mutation.data.improved_text}</p>
               </div>
             )}
           </div>
@@ -108,17 +109,17 @@ export default function AiWritingHelper({ text, task_type = "ielts_writing" }: P
             <p className="text-xs font-semibold text-primary mb-1 flex items-center gap-1">
               <Sparkles className="h-3 w-3" /> Grammar notes
             </p>
-            {(mutation.data.grammar_notes?.length ?? 0) > 0 ? (
-              mutation.data.grammar_notes!.map((note, i) => (
+            {(mutation.data.changes?.length ?? 0) > 0 ? (
+              mutation.data.changes.map((c, i) => (
                 <div key={i} className="text-sm border-l-2 border-warning pl-2">
-                  <p className="text-muted-foreground">{note}</p>
+                  <p className="text-muted-foreground"><strong>{c.original}</strong> → {c.revised} — {c.reason}</p>
                 </div>
               ))
             ) : (
               <p className="text-sm text-muted-foreground">No grammar issues flagged.</p>
             )}
-            {mutation.data.feedback ? (
-              <p className="text-xs text-muted-foreground pt-2 border-t">{mutation.data.feedback}</p>
+            {mutation.data.tips?.length > 0 ? (
+              <p className="text-xs text-muted-foreground pt-2 border-t">{mutation.data.tips.join("; ")}</p>
             ) : null}
           </div>
         )}
@@ -128,9 +129,9 @@ export default function AiWritingHelper({ text, task_type = "ielts_writing" }: P
             <p className="text-xs font-semibold text-primary mb-1 flex items-center gap-1">
               <Sparkles className="h-3 w-3" /> Estimated band / assessment
             </p>
-            <p className="text-sm text-muted-foreground">{mutation.data.feedback}</p>
-            {mutation.data.improved ? (
-              <p className="text-sm mt-2 pt-2 border-t">{mutation.data.improved}</p>
+            <p className="text-sm text-muted-foreground">{mutation.data.tips?.join(" ") ?? ""}</p>
+            {mutation.data.improved_text ? (
+              <p className="text-sm mt-2 pt-2 border-t">{mutation.data.improved_text}</p>
             ) : null}
           </div>
         )}