Update docs and screenshots

backend/alembic/versions/20260722_0003_scene_targets.py

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+"""Add persisted scene targets."""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "20260722_0003"
+down_revision = "20260719_0002"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    tables = set(inspector.get_table_names())
+    if "scenes" not in tables:
+        return
+
+    columns = {column["name"] for column in inspector.get_columns("scenes")}
+    if "targets" not in columns:
+        with op.batch_alter_table("scenes") as batch_op:
+            batch_op.add_column(
+                sa.Column(
+                    "targets",
+                    sa.JSON(),
+                    nullable=False,
+                    server_default=sa.text("'[]'"),
+                )
+            )
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    tables = set(inspector.get_table_names())
+    if "scenes" not in tables:
+        return
+
+    columns = {column["name"] for column in inspector.get_columns("scenes")}
+    if "targets" in columns:
+        with op.batch_alter_table("scenes") as batch_op:
+            batch_op.drop_column("targets")