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/auth_sessions_001.py

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+"""auth_sessions table, so sign-out and password changes revoke JWTs
+
+Revision ID: auth_sessions_001
+Revises: agent_quick_replies_001
+Create Date: 2026-10-12
+
+Tokens issued before this revision carry no session id and stay valid until
+they expire, so the deploy signs nobody out.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = 'auth_sessions_001'
+down_revision: Union[str, None] = 'agent_quick_replies_001'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        'auth_sessions',
+        sa.Column('id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('user_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('created_at', sa.DateTime(timezone=True),
+                  server_default=sa.text('now()'), nullable=True),
+        sa.Column('revoked_at', sa.DateTime(timezone=True), nullable=True),
+        sa.ForeignKeyConstraint(['user_id'], ['users.id'], ondelete='CASCADE'),
+        sa.PrimaryKeyConstraint('id'),
+    )
+    op.create_index('ix_auth_sessions_user_id', 'auth_sessions', ['user_id'])
+
+
+def downgrade() -> None:
+    op.drop_index('ix_auth_sessions_user_id', table_name='auth_sessions')
+    op.drop_table('auth_sessions')