Slovak (sk) translation added

[matusformanek]

Add Slovak (sk) translation

Description

Adds a complete Slovak translation of the DSpace Angular UI (src/assets/i18n/sk.json5),
translated from the English source with the Czech (cs) translation used as a secondary reference.

What's included

• All 3943 keys translated, matching en.json5 1:1 (no missing/extra keys, identical order).
• Previously untranslated // TODO New key entries are now translated (media type, ORCID,
  COAR Notify / LDN services, bitstream replace/related, audio/video transcript, etc.).
• Consistent terminology (e.g. bitstream → „súbor", policies → „pravidlá",
  EPerson → „používateľ", submitter → „vkladateľ", namespace → „menný priestor").
• All {{ placeholder }} variables and HTML tags preserved unchanged.

Validation

• Validated as JSON5 (parses cleanly).
• Key-level diff against en.json5: 0 missing, 0 extra, identical order, 0 duplicates,
  0 placeholder mismatches.

Notes

• Deployment-specific defaults (repository.title, info.end-user-agreement.hosting-country)
  use generic/Slovak placeholders that instances can override.

[milanmajchrak]

@tdonohue We at dataquest can review this PR, as we are based in Slovakia.