feat(mcp): friendly UI message when stdio MCP refused by Box state

Previously the MCP detail dialog dumped the raw RuntimeError text from
``_init_stdio_python_server`` — English-only, prefixed with "Failed
after 4 attempts", and exposing internal config names. The retry
wrapper also kept retrying a refusal that is deterministically going
to fail again, polluting logs.

Replace the raw text with a structured signal:

- New ``MCPSessionErrorPhase.BOX_UNAVAILABLE`` enum value. The stdio
  refusal path sets it before raising and uses a short opaque
  discriminator (``box_disabled_in_config`` / ``box_unavailable``) as
  the message body — never user-facing
- ``_lifecycle_loop_with_retry`` short-circuits on
  ``BOX_UNAVAILABLE``: surfaces the error immediately, no retries,
  no "Failed after N attempts" prefix. Silences the warning storm
  seen during smoke-testing
- ``MCPServerRuntimeInfo`` (TS type) now declares ``error_phase``,
  ``retry_count``, ``box_session_id``, ``box_enabled`` to match what
  the backend already returns in get_runtime_info_dict()
- Both MCP detail forms (``mcp/components/mcp-form/MCPForm.tsx`` and
  ``plugins/mcp-server/mcp-form/MCPFormDialog.tsx``) detect
  ``error_phase === 'box_unavailable'`` and render a two-line
  localized notice: state line ("Box disabled / unreachable") plus
  remediation line ("enable Box or switch to http/sse")
- 8 locale files (en/zh-Hans/zh-Hant/ja/ru/vi/th/es) get
  ``mcp.boxDisabledStdioRefused``, ``mcp.boxUnavailableStdioRefused``,
  ``mcp.boxStdioRefusedSuggestion``

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/i18n/locales/zh-Hans.ts

@@ -710,6 +710,12 @@ const zhHans = {
     connectionSuccess: '连接成功',
     connectionFailed: '连接失败，请检查URL',
     connectionFailedStatus: '连接失败',
+    boxDisabledStdioRefused:
+      'Stdio 模式的 MCP 服务器依赖 Box 沙箱，目前已在配置中禁用（box.enabled = false）。',
+    boxUnavailableStdioRefused:
+      'Stdio 模式的 MCP 服务器依赖 Box 沙箱，目前无法连接。',
+    boxStdioRefusedSuggestion:
+      '请启用 Box（box.enabled = true）并确认运行时连接正常，或将此服务器切换到 http/sse 模式。',
     toolsFound: '个工具',
     unknownError: '未知错误',
     noToolsFound: '未找到任何工具',