Backend efficiency & consistency pass

- Rewrite get_all_tags() with SQL unnest instead of loading all notes
- Consolidate convert_note_to_task/convert_task_to_note to single-session ops
- Add search_notes_for_context() with single OR-keyword query for build_context()
- Drop selectinload from list_conversations(), use correlated subquery for message_count
- Add set_settings_batch() for single-transaction multi-setting upserts
- Extract get_installed_models() shared helper into services/llm.py
- Delete services/tasks.py pass-through wrapper; routes/tasks.py imports from services.notes
- Add B-tree indexes on notes.title and conversations.updated_at (migration 0007)
- Add logging to services/notes.py, services/chat.py, services/settings.py
- Safe Conversation.to_dict() when messages relationship is not loaded

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

src/fabledassistant/routes/chat.py

@@ -29,7 +29,7 @@ async def list_conversations_route():
     offset = request.args.get("offset", 0, type=int)
     conversations, total = await list_conversations(limit=limit, offset=offset)
     return jsonify({
-        "conversations": [c.to_dict() for c in conversations],
+        "conversations": conversations,
         "total": total,
     })
 
@@ -180,7 +180,7 @@ async def chat_status_route():
             resp.raise_for_status()
             result["ollama"] = "available"
             data = resp.json()
-            model_names = [m["name"] for m in data.get("models", [])]
+            model_names = {m["name"] for m in data.get("models", [])}
             # Match with or without :latest tag
             if default_model in model_names or f"{default_model}:latest" in model_names:
                 result["model"] = "ready"