fix(ui): localize project flows and theme settings colors

[vickioo]

Summary

• Replace the duplicate top language dropdown with the existing segmented language switch UI and remove the later duplicate language block.
• Move provider upstream settings and shared switches onto theme tokens so light/custom color profiles are respected.
• Localize New Project, project menu actions, and project context editing dialogs, including zh-CN strings, and pass locale through the project UI chain.

Upstream/release check

• Open upstream PRs checked before this patch: fix(theme): adapt project context modal to light mode #220 (project context light theme) and chore: sync package lock version #221 (lockfile version sync).
• Latest upstream release checked: v0.1.8. These i18n/settings color fixes are not covered by the current release package.
• This PR intentionally includes the project context modal theme-token fix so the unified patch is complete from origin/main, though it overlaps the narrow fix(theme): adapt project context modal to light mode #220 surface.

Validation

• npm run verify:theme-tokens
• npx eslint src/App.jsx src/components/NewProjectModal.jsx src/components/ProjectContextModal.jsx src/components/ProjectGroup.jsx src/components/Settings.jsx src/components/Sidebar.jsx src/i18n/index.js
• npm run build

Notes

• Full npm run lint still fails on pre-existing unrelated files such as chat.jsx, ValueControlBlock.jsx, and pm-components; this patch keeps those out of scope.