Fix bugs, N+1 queries, and wire settings in persian-tutor

- Replace inline __import__("datetime").timedelta hack with proper import
- Remove unused import random in anki_export.py
- Add error handling for Claude CLI subprocess failures in ai.py
- Fix hardcoded absolute path in stt.py with relative Path resolution
- Fix N+1 DB queries in vocab.get_flashcard_batch and dashboard.get_category_breakdown
  by adding db.get_all_word_progress() batch query
- Wire Ollama model and Whisper size settings to actually update config
  via ai.set_ollama_model() and stt.set_whisper_size()

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

python/persian-tutor/db.py

@@ -2,7 +2,7 @@
 
 import json
 import sqlite3
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 from pathlib import Path
 
 import fsrs
@@ -148,6 +148,13 @@ def get_word_counts(total_vocab_size=0):
     }
 
 
+def get_all_word_progress():
+    """Return all word progress as a dict of word_id -> progress dict."""
+    conn = get_connection()
+    rows = conn.execute("SELECT * FROM word_progress").fetchall()
+    return {row["word_id"]: dict(row) for row in rows}
+
+
 def record_quiz_session(category, total_questions, correct, duration_seconds):
     """Log a completed flashcard session."""
     conn = get_connection()
@@ -203,7 +210,7 @@ def get_stats():
     today = datetime.now(timezone.utc).date()
     for i, row in enumerate(days):
         day = datetime.fromisoformat(row["d"]).date() if isinstance(row["d"], str) else row["d"]
-        expected = today - __import__("datetime").timedelta(days=i)
+        expected = today - timedelta(days=i)
         if day == expected:
             streak += 1
         else: