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/widget_key_lookup_001.py

@@ -0,0 +1,34 @@
+"""Look widget API keys up by a SHA-256 of the key
+
+Checking a key used to bcrypt it against every active widget app, about
+100ms each, on the request's event loop, so each wrong key stalled the API
+in proportion to the number of apps. widget_apps.api_key_lookup holds a
+SHA-256 of the key (safe for a 256-bit random secret) so a key is one
+indexed lookup. Keys issued earlier stay NULL until they are next used.
+
+Revision ID: widget_key_lookup_001
+Revises: session_conversation_key_001
+Create Date: 2026-10-19
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = 'widget_key_lookup_001'
+down_revision: Union[str, None] = 'session_conversation_key_001'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+INDEX_NAME = 'ix_widget_apps_api_key_lookup'
+
+
+def upgrade() -> None:
+    op.add_column('widget_apps', sa.Column('api_key_lookup', sa.String(64), nullable=True), if_not_exists=True)
+    op.create_index(INDEX_NAME, 'widget_apps', ['api_key_lookup'], unique=True, if_not_exists=True)
+
+
+def downgrade() -> None:
+    op.drop_index(INDEX_NAME, table_name='widget_apps', if_exists=True)
+    op.drop_column('widget_apps', 'api_key_lookup', if_exists=True)