feat(db): add first_byte_time_ms column to usage table

alembic/versions/20251215_1707_180e63a9c83a_add_first_byte_time_ms_to_usage_table.py

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+"""add first_byte_time_ms to usage table
+
+Revision ID: 180e63a9c83a
+Revises: e9b3d63f0cbf
+Create Date: 2025-12-15 17:07:44.631032+00:00
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '180e63a9c83a'
+down_revision = 'e9b3d63f0cbf'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    """应用迁移：升级到新版本"""
+    # 添加首字时间字段到 usage 表
+    op.add_column('usage', sa.Column('first_byte_time_ms', sa.Integer(), nullable=True))
+
+
+def downgrade() -> None:
+    """回滚迁移：降级到旧版本"""
+    # 删除首字时间字段
+    op.drop_column('usage', 'first_byte_time_ms')