feat(UI-Overhaul-Phase2): AI Assistent in Kommunikation integriert

Migration 0137: Drop AI chat tables (ai_chat_sessions, ai_chat_messages, ai_chat_attachments, ai_conversations, ai_messages)

Backend:
- Remove AIChatSession, AIChatMessage, AIChatAttachment models from ai_assistant/models.py
- Remove AIConversation, AIMessage from app/models/__init__.py
- Remove session/message/stream/attachment routes from ai_assistant/routes.py
- Add new streaming route POST /ai/conversations/{conversation_id}/stream using comm tables
- Add new messages route GET /ai/conversations/{conversation_id}/messages using comm tables
- Add stream_chat_comm, get_comm_messages, save_comm_message to services.py
- Update external_api.py to use CommConversation/CommMessage instead of AIChatSession/AIChatMessage
- Update unified_search ai_chat_provider to search comm_messages with conversation_type=ai
- Remove ai_copilot router from main.py and routes/__init__.py
- Remove ai_conversation from entity_permissions.py and owner_transfer_service.py
- Update ai_assistant/plugin.py get_entity_models to remove AIChatSession
- Guard ai_copilot_service.py imports with try/except

Frontend:
- Remove AIAssistant.tsx, AIAssistantStandalone.tsx, SessionList.tsx, ChatWindow.tsx
- Remove AI Assistant routes from routes/index.tsx
- Update api/ai.ts: streamChat uses /ai/conversations/{id}/stream, fetchMessages uses /ai/conversations/{id}/messages
- Update Communication.tsx: use convId for AI streaming, remove aiSessionId, use fetchAiMessages for AI conversations
- Update AiChatPanel.tsx: create comm conversation instead of AI session, use new fetchMessages
- Update AISidebar.tsx: remove ChatWindow import, show placeholder

tsc clean, build successful, backend import OK

app/plugins/builtins/ai_assistant/models.py

@@ -134,64 +134,6 @@ class AIAgent(Base, TenantMixin, OwnedMixin):
     config: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict)
 
 
-# --- Chat Sessions ---
-
-class AIChatSession(Base, TenantMixin, OwnedMixin):
-    """Chat session for a user with a specific agent."""
-
-    __tablename__ = "ai_chat_sessions"
-    __table_args__ = (
-        Index("ix_ai_sessions_user", "user_id"),
-        Index("ix_ai_sessions_tenant", "tenant_id"),
-    )
-
-    id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
-    )
-    user_id: Mapped[uuid.UUID] = mapped_column(PGUUID(as_uuid=True), nullable=False)
-    agent_id: Mapped[uuid.UUID | None] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("ai_agents.id", ondelete="SET NULL"),
-        nullable=True,
-    )
-    title: Mapped[str] = mapped_column(String(255), nullable=False, default="Neuer Chat")
-    is_pinned: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
-    is_sidebar: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
-    folder_id: Mapped[uuid.UUID | None] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("ai_chat_folders.id", ondelete="SET NULL"),
-        nullable=True,
-    )
-    sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
-
-
-# --- Chat Messages ---
-
-class AIChatMessage(Base, TenantMixin, OwnedMixin):
-    """Individual message in a chat session."""
-
-    __tablename__ = "ai_chat_messages"
-    __table_args__ = (
-        Index("ix_ai_messages_session", "session_id"),
-        Index("ix_ai_messages_tenant", "tenant_id"),
-    )
-
-    id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
-    )
-    session_id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("ai_chat_sessions.id", ondelete="CASCADE"),
-        nullable=False,
-    )
-    role: Mapped[str] = mapped_column(String(20), nullable=False)
-    content: Mapped[str] = mapped_column(Text, nullable=False, default="")
-    tool_calls: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
-    tool_results: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
-    tokens: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
-    model_used: Mapped[str] = mapped_column(String(200), nullable=False, default="")
-
-
 # --- Chat Folders ---
 
 class AIChatFolder(Base, TenantMixin, OwnedMixin):
@@ -215,34 +157,3 @@ class AIChatFolder(Base, TenantMixin, OwnedMixin):
     )
     user_id: Mapped[uuid.UUID] = mapped_column(PGUUID(as_uuid=True), nullable=False)
     sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
-
-
-# --- Chat Attachments ---
-
-class AIChatAttachment(Base, TenantMixin, OwnedMixin):
-    """File attached to a chat message."""
-
-    __tablename__ = "ai_chat_attachments"
-    __table_args__ = (
-        Index("ix_ai_attachments_message", "message_id"),
-        Index("ix_ai_attachments_session", "session_id"),
-        Index("ix_ai_attachments_tenant", "tenant_id"),
-    )
-
-    id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
-    )
-    message_id: Mapped[uuid.UUID | None] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("ai_chat_messages.id", ondelete="CASCADE"),
-        nullable=True,
-    )
-    session_id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("ai_chat_sessions.id", ondelete="CASCADE"),
-        nullable=False,
-    )
-    filename: Mapped[str] = mapped_column(String(255), nullable=False)
-    mime_type: Mapped[str] = mapped_column(String(255), nullable=False, default="application/octet-stream")
-    size_bytes: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
-    storage_path: Mapped[str] = mapped_column(String(1024), nullable=False)