refactor(www): stabilize locale routing

[akronb]

Issue for this PR

Closes #16278, closes #15984, closes #15194, closes #15904, closes #14997, closes #14409

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR fixes the docs locale architecture introduced in #12508, which made routing dependent on ambient locale state and treated English as a special-case root path. Rather than continuing to patch symptoms (#13109, #13608), this change addresses the root cause: docs URLs are now path-authoritative, English is promoted to an explicit en locale.

Key changes:

• switch Starlight config from defaultLocale: "root" to defaultLocale: "en"
• move English docs content into packages/web/src/content/docs/en/
• add shared docs locale helpers in packages/web/src/lib/docs-locale.ts
• update web middleware to:
  • redirect /docs -> /docs/<locale>/
  • redirect /docs/<slug> -> /docs/<locale>/<slug>
  • normalize legacy /docs/... to /docs/en/...
  • keep explicit locale routes authoritative and refresh oc_locale
• simplify console docs routing by centralizing proxy logic in packages/console/app/src/lib/docs.ts
• update docs sync/update workflows and agent prompts to use the new English docs path

How did you verify your code works?

I verified this with targeted regression tests and package checks:

• added console coverage for docs locale resolution in packages/console/app/test/language.test.ts
• added web coverage for docs redirects and cookie handling in packages/web/test/middleware.test.ts, including English, non-English, legacy root, and unknown locale-like paths
• ran bun test test/language.test.ts in packages/console/app
• ran bun test test/middleware.test.ts in packages/web
• ran bun run astro check in packages/web
• ran bun run typecheck in packages/console/app

I also verified that the docs sync workflow and docs/translator agent references now point at the new English docs source path under packages/web/src/content/docs/en/.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[akronb]

@adamdotdevin could you take a look?