build: 打通 FastAPI 与 Vue 最小工程、依赖与数据库连接

后端入口、配置、Redis 与 Alembic 迁移就位；前端 Vite 工程可安装可构建。

backend/alembic/versions/d4e5f6a7b8c9_add_customer_merge.py

@@ -0,0 +1,37 @@
+"""add customers.merged_into_customer_id for visitor→customer merge
+
+Revision ID: d4e5f6a7b8c9
+Revises: c3d4e5f6a7b8
+Create Date: 2026-07-08
+
+When an anonymous widget visitor shares an email that already belongs to an
+existing customer in the org, the visitor row is merged into that customer.
+The old row keeps a pointer so stale device tokens resolve to the target.
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = 'd4e5f6a7b8c9'
+down_revision = 'c3d4e5f6a7b8'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'customers',
+        sa.Column('merged_into_customer_id', postgresql.UUID(as_uuid=True), nullable=True),
+    )
+    op.create_foreign_key(
+        'fk_customers_merged_into', 'customers', 'customers',
+        ['merged_into_customer_id'], ['id'],
+    )
+    op.create_index('ix_customers_merged_into', 'customers', ['merged_into_customer_id'])
+
+
+def downgrade() -> None:
+    op.drop_index('ix_customers_merged_into', table_name='customers')
+    op.drop_constraint('fk_customers_merged_into', 'customers', type_='foreignkey')
+    op.drop_column('customers', 'merged_into_customer_id')