feat: 完成T-403结果回写与汇总

新增excel.write_back_results，按原Excel文件、工作表和行号回写新标题、新封面图片路径与更新状态。

③更新完成后自动用WriteBackWorker(mode=results)回写结果，并弹窗汇总成功、失败、略过数量；文件被占用时提示关闭Excel后手动重试。

补充Excel结果回写、GUI自动回写/汇总/锁文件提示和模块契约测试，同步任务看板、API、流程和当前状态文档。

app/excel.py

@@ -32,7 +32,10 @@ OUTPUT_HEADERS = {
     "update_status": "更新状态",
 }
 OLD_WRITE_BACK_FIELDS = ("old_title", "old_cover_path")
+RESULT_WRITE_BACK_FIELDS = ("new_title", "new_cover_path", "update_status")
 WRITEABLE_STAGES = {"collected", "generated", "applied"}
+RESULT_WRITEABLE_STAGES = {"generated", "applied"}
+RESULT_WRITEABLE_STATUSES = {"failed", "skipped", "cancelled"}
 LOCK_WINERRORS = {5, 32, 33}
 LOCK_ERRNOS = {13, 16}
 
@@ -310,7 +313,21 @@ def _filter_tasks_by_excel_path(tasks, excel_path):
     return filtered
 
 
+def _is_result_fields(fields) -> bool:
+    return any(field in RESULT_WRITE_BACK_FIELDS for field in fields)
+
+
 def _has_write_back_data(task, fields) -> bool:
+    if _is_result_fields(fields):
+        if getattr(task, "stage", None) in RESULT_WRITEABLE_STAGES:
+            return True
+        if getattr(task, "status", None) in RESULT_WRITEABLE_STATUSES:
+            return True
+        return any(
+            getattr(task, field, None) not in (None, "")
+            for field in ("new_title", "new_cover_path")
+            if field in fields
+        )
     if getattr(task, "stage", None) in WRITEABLE_STAGES:
         return True
     return any(getattr(task, field, None) not in (None, "") for field in fields)
@@ -367,6 +384,32 @@ def _ensure_output_columns(sheet, fields):
     return columns
 
 
+def _update_status(task) -> str:
+    error = getattr(task, "last_error", None)
+    status = getattr(task, "status", None)
+    stage = getattr(task, "stage", None)
+    committed = bool(getattr(task, "committed", 0))
+    if stage == "applied" and committed:
+        return "成功"
+    if status == "failed":
+        return f"失败：{error}" if error else "失败"
+    if status == "skipped":
+        return f"略过：{error}" if error else "略过"
+    if status == "running":
+        return "处理中"
+    if status == "cancelled":
+        return f"已取消：{error}" if error else "已取消"
+    if stage == "generated":
+        return "待更新"
+    return ""
+
+
+def _field_value(task, field):
+    if field == "update_status":
+        return _update_status(task)
+    return getattr(task, field, None) or ""
+
+
 def _write_tasks_to_workbook(workbook, tasks, fields) -> int:
     rows = 0
     missing_sheets = []
@@ -387,7 +430,7 @@ def _write_tasks_to_workbook(workbook, tasks, fields) -> int:
                 sheet.cell(
                     row=int(task.source_row),
                     column=columns[field],
-                ).value = getattr(task, field, None) or ""
+                ).value = _field_value(task, field)
             rows += 1
 
     if missing_sheets:
@@ -450,6 +493,21 @@ def write_back(batch_id, excel_path=None, path=None) -> dict:
     )
 
 
+def write_back_results(batch_id, excel_path=None, path=None) -> dict:
+    """Write generated title/cover and update status back to the original Excel file."""
+
+    _require_openpyxl()
+    fields = RESULT_WRITE_BACK_FIELDS
+    tasks = _filter_tasks_by_excel_path(_batch_tasks(batch_id, path=path), excel_path)
+    groups = _group_by_source_file(tasks, fields)
+    return _write_result(
+        batch_id,
+        groups,
+        lambda source_path: source_path,
+        fields,
+    )
+
+
 def _is_excel_output_path(path_value) -> bool:
     return _excel_suffix(path_value) in {".xlsx", ".xlsm"}