feat: non-blocking updates — download in app, apply at launch

Startup no longer blocks on a download. New split:
- services/installer.py: download_and_stage() (runs while the app is open →
  staging\app.new, verified) and apply_staged() (launcher swaps it into app\
  at next launch, when the exe isn't locked).
- launcher.py: slimmed to seed + apply_staged + launch; no network at startup.
- main_window: a new version lights a dot on the ⚙ 配置 button instead of a
  blocking banner; the old open-folder banner is removed.
- settings_dialog: "检查并更新" downloads + stages, then "下次启动生效".

Verified end-to-end over a local HTTP server (download→stage→apply); 101 tests
pass (test_installer +11, test_launcher rewritten).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/widgets/settings_dialog.py

@@ -20,24 +20,34 @@ from PySide6.QtWidgets import (
 )
 
 from version import APP_VERSION
-from services.update_service import is_newer, load_manifest
+from services.file_service import get_app_dir
+from services import installer
+from services.update_service import check_for_update, is_newer, load_manifest
 
 logger = logging.getLogger(__name__)
 
 
 class SettingsDialog(QDialog):
-    """Edit update_source / update_user / update_pass with a connection test."""
+    """Edit update config; test the connection; download+stage an update.
 
-    _test_done = Signal(str)   # result message, delivered to the UI thread
+    Downloading happens here (app is running, writes to staging\\app.new); the
+    actual app/app.old swap is applied by the launcher on the next start, since
+    Windows locks the running exe (docs/10-lan-update.md).
+    """
+
+    _test_done = Signal(str)     # connection-test result message (UI thread)
+    _update_done = Signal(bool, str)   # (ok, message) after download+stage
 
     def __init__(self, parent=None, *, update_source="", update_user="",
-                 update_pass="", current_version=APP_VERSION):
+                 update_pass="", current_version=APP_VERSION, update_info=None):
         super().__init__(parent)
         self.setWindowTitle("设置")
         self.setMinimumWidth(420)
         self._current_version = current_version
+        self._update_info = update_info
         self._setup_ui(update_source, update_user, update_pass)
         self._test_done.connect(self._on_test_done)
+        self._update_done.connect(self._on_update_done)
 
     # ── UI ───────────────────────────────────────────────────────────────────
 
@@ -83,7 +93,19 @@ class SettingsDialog(QDialog):
         self._result.setWordWrap(True)
         col.addWidget(self._result)
 
-        hint = QLabel("提示：建议使用只读账号；生产环境请走 HTTPS（凭据为明文存储）。")
+        # ── update section ───────────────────────────────────────────────────
+        update_row = QHBoxLayout()
+        self._update_status = QLabel(self._update_status_text())
+        self._update_status.setObjectName("settingsUpdate")
+        self._update_status.setWordWrap(True)
+        update_row.addWidget(self._update_status, 1)
+        self._update_btn = QPushButton("检查并更新")
+        self._update_btn.clicked.connect(self._on_update)
+        update_row.addWidget(self._update_btn)
+        col.addLayout(update_row)
+
+        hint = QLabel("提示：建议使用只读账号；生产环境请走 HTTPS（凭据为明文存储）。"
+                      "更新下载完成后，下次启动时自动生效。")
         hint.setObjectName("settingsHint")
         hint.setWordWrap(True)
         col.addWidget(hint)
@@ -144,3 +166,40 @@ class SettingsDialog(QDialog):
     def _on_test_done(self, msg):
         self._result.setText(msg)
         self._test_btn.setEnabled(True)
+
+    # ── manual update: download + stage (swap applied by launcher next start) ──
+
+    def _update_status_text(self):
+        if self._update_info:
+            return "发现新版本 v{}（当前 v{}）。".format(
+                self._update_info.version, self._current_version)
+        return "当前 v{}。".format(self._current_version)
+
+    def _on_update(self):
+        source = self._source_edit.text().strip()
+        if not source:
+            self._update_status.setText("请先填写更新地址。")
+            return
+        user, password = self._user_edit.text(), self._pass_edit.text()
+        install_root = installer.install_root_for(get_app_dir())
+        self._update_btn.setEnabled(False)
+        self._update_status.setText("正在下载…")
+
+        def worker():
+            try:
+                info = check_for_update(source, self._current_version, user, password)
+                if info is None:
+                    self._update_done.emit(True, "已是最新版本（或更新源不可用）。")
+                    return
+                installer.download_and_stage(install_root, info, user, password)
+                self._update_done.emit(
+                    True, "已下载 v{}，下次启动时自动更新。".format(info.version))
+            except Exception as exc:
+                logger.info("Update download failed: %s", exc)
+                self._update_done.emit(False, "更新失败：{}".format(exc))
+
+        threading.Thread(target=worker, name="settings-update", daemon=True).start()
+
+    def _on_update_done(self, ok, msg):
+        self._update_status.setText(msg)
+        self._update_btn.setEnabled(True)