Data groups: a provider's models read only their own group's data

Every connection is in a data group. Its models are handed, and can find,
only that group's memories, notes, skills, knowledge, reports and
personality -- by search and by id. A chat stays in the group it was
started in: switching its model, the endpoint fallback, the crowd, friends,
bases and the @ menu all stay inside it, and a chat whose model has moved
is refused rather than sent. A group may name its own embedder and image
reviewer. data.manage lets a person make personal groups, remap
connections for themselves and move their own records.

Also: a search no longer mixes two embedders of the same width.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lembas/db/models/chat.py

@@ -17,6 +17,7 @@ from sqlalchemy import (
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+from lembas.db.models.data_group import InDataGroup
 from lembas.db.types import JSONDict, JSONList
 
 if TYPE_CHECKING:
@@ -173,7 +174,7 @@ class Folder(UUIDPrimaryKey, Timestamps, Base):
         return f"<Folder {self.name}>"
 
 
-class Chat(UUIDPrimaryKey, Timestamps, Base):
+class Chat(UUIDPrimaryKey, Timestamps, InDataGroup, Base):
     __tablename__ = "chats"
 
     user_id: Mapped[str] = mapped_column(