feat: 更新首页信息处理模型，支持内存缓存与过期机制；添加全量目录同步脚本

backend/migrations/versions/0017_remove_message_cache.py

@@ -0,0 +1,18 @@
+"""Remove persisted announcement sources and interpretations; use memory only."""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0017"
+down_revision = "0016"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    cache = sa.table("home_information", sa.column("resource", sa.String()))
+    op.execute(cache.delete().where(cache.c.resource.like("messages:%")))
+
+
+def downgrade():
+    # Platform cache is reproducible; deleted text and interpretations are not restored.
+    pass