Add turn configuration support for assistants

- Introduce a new `turnConfig` field in `AssistantConfig` and `Assistant` models to manage user interaction settings.
- Implement `TurnConfig`, `BargeInConfig`, `VadConfig`, and `TurnDetectionConfig` schemas to define turn management strategies.
- Update the backend to handle turn configuration in the database and during assistant operations.
- Enhance frontend components with a `TurnConfigEditor` for configuring turn settings, including VAD and barge-in strategies.
- Modify existing pages to integrate turn configuration, improving user experience and interaction capabilities.

backend/migrations/versions/20260712_0004_add_turn_config.py

@@ -0,0 +1,25 @@
+"""add assistant turn configuration
+
+Revision ID: 20260712_0004
+Revises: 20260710_0003
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "20260712_0004"
+down_revision = "20260710_0003"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "assistants",
+        sa.Column("turn_config", sa.JSON(), server_default=sa.text("'{}'"), nullable=False),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("assistants", "turn_config")