Worker di visione per stazione: modello, API, migrazione 019, execute_task (#45)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NABedeMX43pyXZbDNUgA5B

src/backend/migrations/versions/019_station_vision_worker.py

@@ -0,0 +1,34 @@
+"""stations.vision_worker_url e vision_results.worker_url (#45)
+
+stations.vision_worker_url: worker di visione della stazione (NULL = centrale).
+vision_results.worker_url: worker effettivamente chiamato per quel risultato.
+
+Revision ID: 019_station_vision_worker
+Revises: 018_task_loop_results
+Create Date: 2026-10-11
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '019_station_vision_worker'
+down_revision: Union[str, None] = '018_task_loop_results'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # batch_alter_table come nelle migrazioni vicine: serve a SQLite
+    with op.batch_alter_table('stations') as batch:
+        batch.add_column(sa.Column('vision_worker_url', sa.String(500), nullable=True))
+    with op.batch_alter_table('vision_results') as batch:
+        batch.add_column(sa.Column('worker_url', sa.String(500), nullable=True))
+
+
+def downgrade() -> None:
+    with op.batch_alter_table('vision_results') as batch:
+        batch.drop_column('worker_url')
+    with op.batch_alter_table('stations') as batch:
+        batch.drop_column('vision_worker_url')