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/settings.py

@@ -1,29 +1,11 @@
-import httpx
 from quart import Blueprint, jsonify, request
 
-from fabledassistant.config import Config
-from fabledassistant.services.settings import get_all_settings, set_setting
+from fabledassistant.services.llm import get_installed_models
+from fabledassistant.services.settings import get_all_settings, set_settings_batch
 
 settings_bp = Blueprint("settings", __name__, url_prefix="/api/settings")
 
 
-async def _get_installed_models() -> set[str]:
-    """Return set of installed Ollama model names, with and without :latest."""
-    try:
-        async with httpx.AsyncClient(timeout=5.0) as client:
-            resp = await client.get(f"{Config.OLLAMA_URL}/api/tags")
-            resp.raise_for_status()
-            data = resp.json()
-            names: set[str] = set()
-            for m in data.get("models", []):
-                name = m["name"]
-                names.add(name)
-                names.add(name.replace(":latest", ""))
-            return names
-    except Exception:
-        return set()
-
-
 @settings_bp.route("", methods=["GET"])
 async def get_settings_route():
     settings = await get_all_settings()
@@ -38,11 +20,10 @@ async def update_settings_route():
 
     if "default_model" in data:
         model = str(data["default_model"])
-        installed = await _get_installed_models()
+        installed = await get_installed_models()
         if installed and model not in installed:
             return jsonify({"error": f"Model '{model}' is not installed"}), 400
 
-    for key, value in data.items():
-        await set_setting(key, str(value))
+    await set_settings_batch({k: str(v) for k, v in data.items()})
     settings = await get_all_settings()
     return jsonify(settings)