fix: move declaration to after runtime flags for positional compat

DouyinVideoUploadRequest dataclass 声明字段位置
被独立审查者（deleg_61d33c80）标记为P1兼容问题：
旧位置调用 ('scheduled', False, False) 会被错位解析。

把 declaration 移到最后，保留旧位置契约。

Previous-Review: deleg_61d33c80
Ref: dreammis/social-auto-upload#213（安全后续修正）

sau_cli.py

@@ -63,10 +63,10 @@ class DouyinVideoUploadRequest:
     thumbnail_portrait_file: Path | None = None
     product_link: str = ""
     product_title: str = ""
-    declaration: str | None = None
     publish_strategy: str = DOUYIN_PUBLISH_STRATEGY_IMMEDIATE
     debug: bool = True
     headless: bool = True
+    declaration: str | None = None
 
 
 @dataclass(slots=True)