feat(branding): rebrand user-facing GPUStack to MesaStack

Applied via scripts/rebrand across UI labels, page title, and all
locale strings (en/zh/ja/ru/tr). Functional references untouched:
npm package, URLs, paths, JS identifiers, GPUSTACK_ constants, and the
X-GPUStack-Model header. The backend-contract startsWith string in
llmodels/hooks keeps "GPUStack server" to stay matchable. Logo images
intentionally left unchanged for now.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/locales/zh-CN/common.ts

@@ -44,7 +44,7 @@ export default {
   'common.button.rollback': '回滚',
   'common.button.new': '新建{ text }',
   'common.button.upgrade': '升级',
-  'common.enterprise.feature': 'GPUStack 企业版可用',
+  'common.enterprise.feature': 'MesaStack 企业版可用',
   'common.input.holder': '请输入',
   'common.holder.search': '搜索',
   'common.button.edit': '编辑',