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/session_conversation_key_001.py

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+"""Scope widget conversations and customers to the token that created them
+
+A widget token the visitor obtained without proving who they are may name an
+existing customer. session_to_agents.conversation_key records which token scope
+created a session, so such a token only resumes its own conversations; existing
+rows stay NULL, the scope of tokens the embedding app vouched for.
+customers.conversation_key records which widget scope created a customer, so a
+token may only edit or merge a customer it created itself.
+
+Every scope check filters session_to_agents by customer_id, which had no index;
+the index is built CONCURRENTLY so the table keeps taking writes while the
+backend starts. That can't run in a transaction, hence the autocommit block. A
+build that fails part-way leaves an INVALID index that IF NOT EXISTS would then
+skip: if that happens, DROP INDEX ix_session_to_agents_customer_id and restart.
+
+Revision ID: session_conversation_key_001
+Revises: auth_sessions_001
+Create Date: 2026-10-12
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+# Keep revision ids under 32 characters: alembic_version.version_num is
+# varchar(32).
+revision: str = 'session_conversation_key_001'
+down_revision: Union[str, None] = 'auth_sessions_001'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+INDEX_NAME = 'ix_session_to_agents_customer_id'
+
+
+def upgrade() -> None:
+    op.add_column('session_to_agents', sa.Column('conversation_key', sa.String(64), nullable=True),
+                  if_not_exists=True)
+    op.add_column('customers', sa.Column('conversation_key', sa.String(64), nullable=True),
+                  if_not_exists=True)
+    with op.get_context().autocommit_block():
+        op.create_index(
+            INDEX_NAME, 'session_to_agents', ['customer_id'],
+            unique=False,
+            postgresql_concurrently=True,
+            if_not_exists=True,
+        )
+
+
+def downgrade() -> None:
+    with op.get_context().autocommit_block():
+        op.drop_index(INDEX_NAME, table_name='session_to_agents',
+                      postgresql_concurrently=True, if_exists=True)
+    op.drop_column('customers', 'conversation_key', if_exists=True)
+    op.drop_column('session_to_agents', 'conversation_key', if_exists=True)