Add persian-tutor: Gradio-based GCSE Persian language learning app

Vocabulary study with FSRS spaced repetition, AI tutoring (Ollama/Claude),
essay marking, idioms browser, Anki export, and dashboard. 918 vocabulary
entries across 39 categories. 41 tests passing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

python/persian-tutor/modules/essay.py

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+"""Essay writing and AI marking."""
+
+import db
+from ai import ask
+
+MARKING_SYSTEM_PROMPT = """You are an expert Persian (Farsi) language teacher marking a GCSE-level essay.
+You write in English but can read and correct Persian text.
+Always provide constructive, encouraging feedback suitable for a language learner."""
+
+MARKING_PROMPT_TEMPLATE = """Please mark this Persian essay written by a GCSE student.
+
+Theme: {theme}
+
+Student's essay:
+{essay_text}
+
+Please provide your response in this exact format:
+
+**Grade:** [Give a grade from 1-9 matching GCSE grading, or a descriptive level like A2/B1]
+
+**Summary:** [1-2 sentence overview of the essay quality]
+
+**Corrections:**
+[List specific errors with corrections. For each error, show the original text and the corrected version in Persian, with an English explanation]
+
+**Improved version:**
+[Rewrite the essay in corrected Persian]
+
+**Tips for improvement:**
+[3-5 specific, actionable tips for the student]"""
+
+
+GCSE_THEMES = [
+    "Identity and culture",
+    "Local area and environment",
+    "School and work",
+    "Travel and tourism",
+    "International and global dimension",
+]
+
+
+def mark_essay(essay_text, theme="General"):
+    """Send essay to AI for marking. Returns structured feedback."""
+    if not essay_text or not essay_text.strip():
+        return "Please write an essay first."
+
+    prompt = MARKING_PROMPT_TEMPLATE.format(
+        theme=theme,
+        essay_text=essay_text.strip(),
+    )
+
+    feedback = ask(prompt, system=MARKING_SYSTEM_PROMPT, quality="smart")
+
+    # Extract grade from feedback (best-effort)
+    grade = ""
+    for line in feedback.split("\n"):
+        if line.strip().startswith("**Grade:**"):
+            grade = line.replace("**Grade:**", "").strip()
+            break
+
+    # Save to database
+    db.save_essay(essay_text.strip(), grade, feedback, theme)
+
+    return feedback
+
+
+def get_essay_history(limit=10):
+    """Return recent essays for the history view."""
+    essays = db.get_recent_essays(limit)
+    result = []
+    for e in essays:
+        result.append({
+            "Date": e["timestamp"],
+            "Theme": e["theme"] or "General",
+            "Grade": e["grade"] or "-",
+            "Preview": (e["essay_text"] or "")[:50] + "...",
+        })
+    return result