feat(mcp-web): block stdio MCP creation at the form when Box is unavailable

When Box is disabled in config (``box.enabled = false``) or unreachable,
saving a new MCP server in stdio mode produced one that could never
start — the user would only learn that from the runtime error on the
detail page. Stop the user before they save instead.

Both MCP forms (the page-level ``MCPForm.tsx`` and the older dialog
``MCPFormDialog.tsx``) now:

- Disable the ``stdio`` option in the mode select when Box is
  unavailable, with a small "(requires Box)" suffix so the reason is
  obvious. Existing stdio configs still display their current value
- Show ``BoxUnavailableNotice`` inline under the mode select when the
  currently-selected mode is stdio and Box is unavailable, so editing
  a stale stdio config makes the cause visible
- Disable the Save / Submit button while stdio is selected under that
  condition. ``MCPForm`` exposes a new ``onSaveBlockedChange`` prop
  so the parent ``MCPDetailContent`` can disable both its Submit and
  Save buttons. ``MCPFormDialog`` disables its Save button locally
- Refuse the submit handler too (Enter-key path) with a toast carrying
  the same i18n message

i18n: ``mcp.boxRequired`` (short tag in the disabled option) and
``mcp.stdioBlockedByBoxToast`` added to all 8 locales.

Backend runtime gate (``_init_stdio_python_server`` refusal +
``BOX_UNAVAILABLE`` error_phase + retry short-circuit) stays in place
as the last line of defence for API bypass.

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

web/src/i18n/locales/en-US.ts

@@ -744,6 +744,9 @@ const enUS = {
       'Stdio MCP servers require the Box sandbox, which is currently unreachable.',
     boxStdioRefusedSuggestion:
       'Enable Box (box.enabled = true) and ensure the runtime is healthy, or switch this server to http/sse mode.',
+    boxRequired: 'requires Box',
+    stdioBlockedByBoxToast:
+      'Stdio MCP cannot be saved while the Box sandbox is disabled or unreachable. Enable Box or pick http/sse.',
     toolsFound: 'tools',
     unknownError: 'Unknown error',
     noToolsFound: 'No tools found',

web/src/i18n/locales/es-ES.ts

@@ -758,6 +758,9 @@ const esES = {
       'Los servidores MCP en modo stdio requieren el sandbox de Box, actualmente no accesible.',
     boxStdioRefusedSuggestion:
       'Active Box (box.enabled = true) y asegúrese de que el runtime está conectado, o cambie este servidor a modo http/sse.',
+    boxRequired: 'requiere Box',
+    stdioBlockedByBoxToast:
+      'No se puede guardar el MCP en modo stdio mientras el sandbox de Box está desactivado o no disponible. Active Box o seleccione modo http/sse.',
     toolsFound: 'herramientas',
     unknownError: 'Error desconocido',
     noToolsFound: 'No se encontraron herramientas',

web/src/i18n/locales/ja-JP.ts

@@ -749,6 +749,9 @@ const jaJP = {
       'Stdio モードの MCP サーバーは Box サンドボックスを必要としますが、現在接続できません。',
     boxStdioRefusedSuggestion:
       'Box を有効化（box.enabled = true）してランタイムの接続を確認するか、このサーバーを http/sse モードに切り替えてください。',
+    boxRequired: 'Box が必要',
+    stdioBlockedByBoxToast:
+      'Box サンドボックスが無効または利用できないため、stdio モードの MCP は保存できません。Box を有効化するか、http/sse モードに切り替えてください。',
     toolsFound: '個のツール',
     unknownError: '不明なエラー',
     noToolsFound: 'ツールが見つかりません',

web/src/i18n/locales/ru-RU.ts

@@ -754,6 +754,9 @@ const ruRU = {
       'MCP-серверы в режиме stdio требуют песочницу Box, которая сейчас недоступна.',
     boxStdioRefusedSuggestion:
       'Включите Box (box.enabled = true) и убедитесь, что среда работает, либо переключите этот сервер в режим http/sse.',
+    boxRequired: 'требуется Box',
+    stdioBlockedByBoxToast:
+      'Сохранить MCP в режиме stdio нельзя: песочница Box отключена или недоступна. Включите Box либо выберите режим http/sse.',
     toolsFound: 'инструментов',
     unknownError: 'Неизвестная ошибка',
     noToolsFound: 'Инструменты не найдены',

web/src/i18n/locales/th-TH.ts

@@ -734,6 +734,9 @@ const thTH = {
       'MCP server แบบ stdio ต้องใช้ Sandbox Box ซึ่งขณะนี้เชื่อมต่อไม่ได้',
     boxStdioRefusedSuggestion:
       'กรุณาเปิดใช้งาน Box (box.enabled = true) และตรวจสอบว่ารันไทม์ทำงานปกติ หรือเปลี่ยน MCP server เป็นโหมด http/sse',
+    boxRequired: 'ต้องใช้ Box',
+    stdioBlockedByBoxToast:
+      'ไม่สามารถบันทึก MCP โหมด stdio เนื่องจาก Sandbox Box ถูกปิดใช้งานหรือไม่พร้อมใช้งาน กรุณาเปิดใช้งาน Box หรือเลือกโหมด http/sse',
     toolsFound: 'เครื่องมือ',
     unknownError: 'ข้อผิดพลาดที่ไม่ทราบสาเหตุ',
     noToolsFound: 'ไม่พบเครื่องมือ',

web/src/i18n/locales/vi-VN.ts

@@ -748,6 +748,9 @@ const viVN = {
       'MCP server ở chế độ stdio cần Sandbox Box, hiện không thể kết nối.',
     boxStdioRefusedSuggestion:
       'Hãy bật Box (box.enabled = true) và đảm bảo runtime hoạt động, hoặc chuyển server này sang chế độ http/sse.',
+    boxRequired: 'cần Box',
+    stdioBlockedByBoxToast:
+      'Không thể lưu MCP ở chế độ stdio khi Sandbox Box bị tắt hoặc không khả dụng. Hãy bật Box hoặc chọn chế độ http/sse.',
     toolsFound: 'công cụ',
     unknownError: 'Lỗi không xác định',
     noToolsFound: 'Không tìm thấy công cụ nào',

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

@@ -716,6 +716,9 @@ const zhHans = {
       '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。',
+    boxRequired: '需要 Box',
+    stdioBlockedByBoxToast:
+      'Box 沙箱已禁用或不可用，无法保存 stdio 模式的 MCP。请启用 Box 或改为 http/sse 模式。',
     toolsFound: '个工具',
     unknownError: '未知错误',
     noToolsFound: '未找到任何工具',

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

@@ -715,6 +715,9 @@ const zhHant = {
       'Stdio 模式的 MCP 伺服器依賴 Box 沙箱，目前無法連線。',
     boxStdioRefusedSuggestion:
       '請啟用 Box（box.enabled = true）並確認執行時連線正常，或將此伺服器切換到 http/sse 模式。',
+    boxRequired: '需要 Box',
+    stdioBlockedByBoxToast:
+      'Box 沙箱已停用或無法使用，無法儲存 stdio 模式的 MCP。請啟用 Box 或改為 http/sse 模式。',
     toolsFound: '個工具',
     unknownError: '未知錯誤',
     noToolsFound: '未找到任何工具',