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/models/conversation.py

@@ -1,6 +1,7 @@
 from datetime import datetime, timezone
 
 from sqlalchemy import DateTime, ForeignKey, Index, Integer, Text
+from sqlalchemy import inspect
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from fabledassistant.models import Base
@@ -27,12 +28,21 @@ class Conversation(Base):
         order_by="Message.created_at",
     )
 
+    __table_args__ = (
+        Index("ix_conversations_updated_at", "updated_at"),
+    )
+
     def to_dict(self) -> dict:
+        # Use loaded messages if available, otherwise 0
+        if "messages" in inspect(self).dict:
+            msg_count = len(self.messages) if self.messages else 0
+        else:
+            msg_count = 0
         return {
             "id": self.id,
             "title": self.title,
             "model": self.model,
-            "message_count": len(self.messages) if self.messages else 0,
+            "message_count": msg_count,
             "created_at": self.created_at.isoformat(),
             "updated_at": self.updated_at.isoformat(),
         }

src/fabledassistant/models/note.py

@@ -46,6 +46,7 @@ class Note(Base):
     __table_args__ = (
         Index("ix_notes_tags", "tags", postgresql_using="gin"),
         Index("ix_notes_status", "status"),
+        Index("ix_notes_title", "title"),
     )
 
     @property