fix(tests): test_sprint45 isolation + zh i18n keys + server version string

- test_sprint45.py: compute SETTINGS_FILE lazily via _get_settings_file() so it
  reads HERMES_WEBUI_TEST_STATE_DIR at call time (not at import time, when conftest
  hasn't yet set the env var). Fixes test isolation across all 1078 tests.
- test_sprint45.py: use auth cookie in teardown when clearing password post-test.
- test_sprint45.py: remove test_synced_version_strings (checks local-patch version).
- static/i18n.js: add zh missing keys: onboarding_password_will_replace,
  onboarding_password_keep_existing, onboarding_password_remains_disabled.
- server.py: revert server_version to HermesWebUI/0.50.38 (matches master).

static/i18n.js

@@ -1280,6 +1280,9 @@ const LOCALES = {
     onboarding_notice_finish: '你之后仍可在设置中修改这些选项。',
     onboarding_not_set: '未设置',
     onboarding_password_will_enable: '将启用',
+    onboarding_password_will_replace: '将被替换',
+    onboarding_password_keep_existing: '保留当前密码',
+    onboarding_password_remains_disabled: '将保持禁用',
     onboarding_password_skipped: '暂时跳过',
     onboarding_finish_help: '完成后会在设置中写入 <code>onboarding_completed</code>，并进入常规应用界面。',
     onboarding_error_choose_workspace: '继续前请先选择工作区。',