fix: force English output in all LLM prompts regardless of PDF language

Questions, MCQ options, explanations and feedback are now always
generated in English even when the source PDF is in French or another language.

core/evaluator.py

@@ -20,6 +20,7 @@ from model.llm import get_llm
 
 _PROMPT_EN = """\
 You are a patient and constructive university tutor.
+IMPORTANT: Always write your entire response in English, even if the source material or student answer is in another language.
 
 Source material:
 {chunk}
@@ -36,36 +37,13 @@ Evaluate the answer using this exact structure:
 3. What was missing or imprecise.
 4. A concise model answer (2-4 sentences).
 
-Be encouraging and specific."""
-
-_PROMPT_FR = """\
-Tu es un tuteur universitaire patient et constructif.
-
-Matériel source :
-{chunk}
-
-Question posée à l'étudiant :
-{question}
-
-Réponse de l'étudiant :
-{answer}
-
-Évalue la réponse en respectant exactement cette structure :
-1. Verdict : Correct / Partiellement correct / Incorrect
-2. Ce qui était bien dans la réponse.
-3. Ce qui manquait ou était imprécis.
-4. Une réponse modèle concise (2-4 phrases).
-
-Sois encourageant et précis."""
-
-_TEMPLATES = {"English": _PROMPT_EN, "Français": _PROMPT_FR}
+Be encouraging and specific. Write in English only."""
 
 
 def evaluate_answer(question: str, chunk: str, student_answer: str, language: str = "English") -> str:
     """Return structured feedback for *student_answer* given *question* and *chunk*."""
     llm = get_llm()
-    template = _TEMPLATES.get(language, _PROMPT_EN)
-    prompt = template.format(
+    prompt = _PROMPT_EN.format(
         chunk=chunk.strip(),
         question=question.strip(),
         answer=student_answer.strip(),

core/questioner.py

@@ -33,7 +33,7 @@ Rules:
 - ONE question only, on ONE concept
 - Maximum 25 words
 - No sub-questions, no "and", no compound questions
-- Write in {language}
+- IMPORTANT: Always write the question in English, even if the source text is in another language
 - Output only the question, nothing else
 
 Excerpt:
@@ -50,7 +50,7 @@ Rules:
 - One clear question, maximum 25 words
 - Exactly 4 options (A, B, C, D), only ONE is correct
 - All wrong options must be plausible — no obviously wrong answers
-- Write in {language}
+- IMPORTANT: Always write everything in English, even if the source text is in another language
 - For each option, write a 1-sentence explanation of why it is correct or incorrect
 
 Output format (use EXACTLY these labels, one per line, nothing else):