Stazioni: camera_url e camera_source, GET /api/stations/by-code/{code} (#72)

Migrazione 020 con le due colonne su stations, campi in modello, schemi e
servizio (validatore http(s) come vision_worker_url), nuova route by-code
dichiarata prima di /{station_id}. Test di migrazione su e giu e di API.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/migrations/versions/020_station_camera.py

@@ -0,0 +1,33 @@
+"""stations.camera_url e stations.camera_source (#72)
+
+stations.camera_url: servizio camera della stazione (vs-gui o equivalente).
+stations.camera_source: sorgente da chiedere al servizio, es. camera:<seriale>
+o camera:folder.
+
+Revision ID: 020_station_camera
+Revises: 019_station_vision_worker
+Create Date: 2026-10-15
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '020_station_camera'
+down_revision: Union[str, None] = '019_station_vision_worker'
+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('camera_url', sa.String(500), nullable=True))
+        batch.add_column(sa.Column('camera_source', sa.String(200), nullable=True))
+
+
+def downgrade() -> None:
+    with op.batch_alter_table('stations') as batch:
+        batch.drop_column('camera_source')
+        batch.drop_column('camera_url')