Split app env ownership

[nighca]

Closes #3299

Summary

• Split app env ownership between xbuilder and account.
• Configure app-level runtime dependencies from app entry points instead of shared env imports.
• Move existing widgets under app xbuilder and keep their output paths unchanged.
• Use VITE_MODE to select Vite build modes in workflows and Dockerfiles, keeping NODE_ENV reserved for the runtime environment.

Deployment Notes

When this change is released, update the Vercel configuration for the xbuilder app:

• Rename the existing NODE_ENV environment variable to VITE_MODE and set it to production-cn where needed.
• Remove the other existing environment variables so the build uses the app-specific .env.* files committed in this project.

Checks

• npm run type-check
• npm run lint
• npm run test -- --run src/models/common/cloud.test.ts src/components/editor/editing.test.ts src/components/editor/editor-state.test.ts
• npm run build
• VITE_MODE=production-cn npm run build
• npm run build:account
• VITE_MODE=production-cn npm run build:account
• npm run dev -- --port 5175 --host 127.0.0.1, opened http://127.0.0.1:5175/ in Chrome and verified XBuilder home loads
• npm run dev:account -- --host 127.0.0.1, opened http://127.0.0.1:5174/ in Chrome and verified Account home loads

[nighca]

对于 staging/production/production-cn，构建时实际的 NODE_ENV 值都是 production（通过 npm script build 控制），之前外部指定 NODE_ENV 为 staging/production/production-cn 的做法是容易造成误解的

这里换成 VITE_MODE，明确是用于控制 vite mode，对应于最终配置文件的选用

[nighca]

.env 的加载本身有一定策略，比如当指定 mode: abc 的时候，.env.abc.local 会优先级高于 .env.abc（详见 .env Files）；考虑到这里 . 用于分隔 mode name 和 local 这样的特殊标识，因此在 mode name 中把原来的 . 换成 -，减少把 .cn 误解为像 .local 这样的特殊标记的可能性

[nighca]

这个机制干掉了，维护这个机制会比较麻烦，依赖这个机制的页面很少；目前只有 admin 页面依赖它，改为由 admin 页面自己去实现了