feat: add configurable vision focus prompts

backend/migrations/versions/20260812_0019_add_vision_focus_prompt.py

@@ -0,0 +1,32 @@
+"""add assistant vision focus prompt
+
+Revision ID: 20260812_0019
+Revises: 20260810_0018
+"""
+
+from collections.abc import Sequence
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "20260812_0019"
+down_revision: str | Sequence[str] | None = "20260810_0018"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "assistants",
+        sa.Column(
+            "vision_focus_prompt",
+            sa.Text(),
+            server_default=sa.text("''"),
+            nullable=False,
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("assistants", "vision_focus_prompt")