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/modules/vocab.py

@@ -84,8 +84,9 @@ def get_flashcard_batch(count=10, category=None):
     remaining = count - len(due_entries)
     if remaining > 0:
         seen_ids = {e["id"] for e in due_entries}
+        all_progress = db.get_all_word_progress()
         # Prefer unseen words
-        unseen = [e for e in pool if e["id"] not in seen_ids and not db.get_word_progress(e["id"])]
+        unseen = [e for e in pool if e["id"] not in seen_ids and e["id"] not in all_progress]
         if len(unseen) >= remaining:
             fill = random.sample(unseen, remaining)
         else: