fix(migrations): riparenta input_duration dopo 003_measurement_interval

Il rebase aveva creato due head Alembic (003_input_duration e
003_measurement_interval entrambi figli di 002): upgrade head all'avvio
del server sarebbe fallito. Rinominata la revision in 004_input_duration
con down_revision 003_measurement_interval — catena di nuovo lineare.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/backend/migrations/versions/004_add_input_duration_ms.py

@@ -0,0 +1,27 @@
+"""add input_duration_ms to measurements
+
+Revision ID: 004_input_duration
+Revises: 003_measurement_interval
+Create Date: 2026-07-28
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '004_input_duration'
+down_revision: Union[str, None] = '003_measurement_interval'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'measurements',
+        sa.Column('input_duration_ms', sa.Integer, nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('measurements', 'input_duration_ms')