Feature (#4347) : Enable language specific DSpace links via lang quer…

[guillermo-escire]

…y param

References

Fixes #4347

Description

Enable DSpace Angular frontend to respect a lang query parameter in the URL.
This allows linking directly to a specific language version (e.g., French, English, Spanish) and ensures the language selector works correctly afterward.

Instructions for Reviewers

List of changes in this PR:

• Added checkQueryParamLanguage() in LocaleService to read lang from the URL and apply it on first load.
• Modified applyLangIfValid() to set the current language and remove the lang query param from the URL.
• Ensured that changing the language via the selector overrides any previously applied URL language.
• Added comments for clarity on private methods.

Testing instructions:

1. Open in a fresh browser or incognito mode.
2. Go to http://localhost:4000/home?lang=fr → page should display in French, URL should remove ?lang=fr.
3. Change the language using the selector → page should stay in the newly selected language.
4. Repeat with ?lang=en and ?lang=es to verify all supported languages.
5. Verify that ESLint passes: npm run lint.
6. Ensure no regression in other DSpace pages.

Checklist

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