feat: 完成Tab④账号管理

- 新增 accounts 服务层，封装账号 CRUD、目录创建、端口分配与登录检测

- 接入 PySide6 账号管理 Tab：表格、账号弹窗、启动登录、后台检测登录

- 密码仅本地保存并在 UI 打码，表格不展示明文；不自动登录或填密码

- 增加顶部 Tab 栏防误点样式，扩大点击区域并高亮当前 Tab

- 补充账号服务和 GUI 单元测试，并同步架构、API、路由、任务和进度文档

app/db.py

@@ -19,6 +19,7 @@ DEFAULT_BUSY_TIMEOUT_MS = 5000
 VALID_BATCH_FIELDS = {"source_files_json", "status", "note"}
 VALID_ACCOUNT_FIELDS = {
     "account_name",
+    "alias",
     "region_host",
     "slug",
     "user_data_dir",
@@ -354,19 +355,24 @@ def add_account(
         return get_account_by_alias(alias, conn=database)
 
 
-def update_account(alias, path=None, conn=None, **fields) -> None:
+def update_account(account_alias, path=None, conn=None, **fields) -> None:
     _validate_fields(fields, VALID_ACCOUNT_FIELDS)
     if not fields:
         return
     fields["updated_at"] = _now()
     assignments = ", ".join(f"{field} = ?" for field in fields)
-    params = list(fields.values()) + [alias]
+    params = list(fields.values()) + [account_alias]
     with _connection(conn, path) as database:
-        with database:
-            database.execute(
-                f"UPDATE accounts SET {assignments} WHERE alias = ?",
-                params,
-            )
+        try:
+            with database:
+                database.execute(
+                    f"UPDATE accounts SET {assignments} WHERE alias = ?",
+                    params,
+                )
+        except sqlite3.IntegrityError as exc:
+            raise DbError(
+                f"账号别名或 slug 已存在: {fields.get('alias', account_alias)}"
+            ) from exc
 
 
 def delete_account(alias, path=None, conn=None) -> None: