fix(windows): reliable service auto-start on boot and start-on-boot GUI entry (#2579)

* fix(service): restart windows service indefinitely on failure

The windows service was installed with only the AutoStart start type
and no SCM failure actions configured. When the service failed during
boot (e.g. network not yet ready, config load error), it reported
SERVICE_STOPPED with a non-zero exit code and stayed stopped until
started manually, which is reported as no auto-start after reboot in
issue #1771.

Configure failure actions on install and update when restart is not
disabled:

- three Restart actions (1s/5s/10s delay) with reset period Never;
  the SCM repeats the last action once the failure count exceeds the
  actions array, so restarts are retried indefinitely
- set fFailureActionsOnNonCrashFailures so exits that report
  SERVICE_STOPPED with a non-zero exit code (the error path in
  win_service_event_loop) are also treated as failures; manual stops
  still exit with 0 and do not trigger a restart

Also exit the service process with a non-zero code after reporting the
error status. Without it the process stayed alive after reporting
SERVICE_STOPPED and was only counted as failed after the SCM
force-killed it, adding roughly 30s of dead time to every retry cycle.

This matches the systemd path, which already generates Restart=always
with StartLimitIntervalSec=0. The --disable-restart-on-failure option
now also clears previously configured failure actions on windows.

Verified on a real windows host: crash failures and reported-error
failures both restart with the configured 1s/5s/10s cadence
indefinitely, manual stops are not restarted, and
--disable-restart-on-failure clears the actions.

* feat(gui): add start-on-boot menu entry pointing to service mode

Issue #1771 reports that users cannot find how to make EasyTier start
on boot. Auto-start is provided by service mode, but the GUI offered
no entry named after it, so the connection was hard to discover.

Add a "Start on Boot" item to the settings menu. It opens the mode
dialog with service mode preselected and shows an info message
explaining that enabling service mode registers EasyTier as a system
service that starts automatically at boot and keeps running in the
background.

When the dialog is opened with service mode preselected, the mode
watcher in ModeSwitcher can run before the default config/log dirs
have been resolved, leaving the fields empty and failing validation on
save. Fill them from the resolved defaults after mount in that case.

Add mode.autostart / mode.autostart_hint strings to the cn/en locales
in frontend-lib.

* fix(cli): stop collecting the --core-args flag into the service args

InstallArgs.core_args was declared without an explicit `long`, so
clap treated it as a trailing positional argument instead of a named
option. Passing `service install --core-args --daemon ...` therefore
collected the literal "--core-args" token into the value, and the
installed service was registered with an invalid command line that
failed on every start (observed on a real windows host: the binPath
contained `easytier-core.exe --core-args --daemon ...`).

Declare it as a real option (`long` + `num_args = 1..`) while keeping
allow_hyphen_values and the trailing semantics: --core-args must be
the last option of install and consumes everything after it.

The bare-positional spelling (`service install --daemon`), the only
correctly-working form before, now fails with a clear "unexpected
argument" error; scripts written against it need to add the
--core-args prefix.

Add unit tests covering the flag, `=` and mixed forms.

easytier-web/frontend-lib/src/locales/cn.yaml

@@ -465,6 +465,8 @@ mode:
   remote_rpc_address_empty: 远程RPC地址不能为空
   service_config_empty: 服务配置不能为空
   rpc_connection_failed: "RPC 连接失败：{error}"
+  autostart: 开机自启
+  autostart_hint: 开机自启由服务模式提供。切换为「服务模式」并保存后，EasyTier 将注册为系统服务，开机自动启动并在后台运行。
 
 config-server:
   title: 配置服务器

easytier-web/frontend-lib/src/locales/en.yaml

@@ -465,6 +465,8 @@ mode:
   remote_rpc_address_empty: Remote RPC Address cannot be empty
   service_config_empty: Service Config cannot be empty
   rpc_connection_failed: "RPC connection failed: {error}"
+  autostart: Start on Boot
+  autostart_hint: Auto-start on boot is provided by service mode. After switching to Service mode and saving, EasyTier will be registered as a system service that starts automatically at boot and keeps running in the background.
 
 config-server:
   title: Config Server