fix(web): sync docs locale cookie on alias redirects

[Seungjun0906]

Closes #13108 #13078 #13057

What does this PR do?

This fixes docs locale reversion when users explicitly navigate via locale aliases (especially /docs/en) while an existing non-English oc_locale cookie is set.
I updated docs middleware to set oc_locale on alias redirects, and normalize root English to oc_locale=en.
I also synced locale changes to oc_locale in app language context so cookie/state stay aligned.
Why this works: docs routing reads oc_locale when deciding redirects from /docs. If cookie and user-selected locale drift, users can bounce back to a previous non-English locale. Keeping cookie synchronized removes that drift.
Note: production /docs/en returning 404 appears to be a front-door routing issue. This PR improves locale consistency once requests reach app/docs logic.

How did you verify your code works?

• Reproduced and checked behavior locally with oc_locale set to non-English values (not only ko).
• Verified /docs/ alias redirect behavior and cookie updates in local docs middleware flow.
• Confirmed changed files are:
  • packages/web/src/middleware.ts
  • packages/app/src/context/language.tsx
• Checked production headers for context:
  • /docs/en returns 404
  • /docs returns 200

[github-actions]

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No duplicate PRs found