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)

tests/test_sau_browser_cli.py

@@ -90,6 +90,16 @@ class BrowserCliParserTests(unittest.TestCase):
             ])
         self.assertIsNone(args.declaration)
 
+    def test_douyin_request_legacy_positional_runtime_flags_keep_their_meaning(self):
+        request = sau_cli.DouyinVideoUploadRequest(
+            "creator", Path("demo.mp4"), "标题", "简介", [], 0,
+            None, None, None, "", "", "scheduled", False, False,
+        )
+        self.assertEqual(request.publish_strategy, "scheduled")
+        self.assertFalse(request.debug)
+        self.assertFalse(request.headless)
+        self.assertIsNone(request.declaration)
+
     def test_tencent_upload_video_accepts_dual_thumbnail_aspects(self):
         with tempfile.TemporaryDirectory() as tmp_dir:
             video_path = Path(tmp_dir) / "demo.mp4"