fix(ActionInsertLink): disable "Link to file" if offline

[mejo-]

Also introduces Playwright and adds tests for offline UI changes.

Fixes: nextcloud/collectives#1868

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.06%. Comparing base (3e1b521) to head (8359f88).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/Menu/ActionInsertLink.vue	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7870      +/-   ##
==========================================
- Coverage   47.10%   47.06%   -0.04%     
==========================================
  Files         141      141              
  Lines        3883     3886       +3     
  Branches      733      733              
==========================================
  Hits         1829     1829              
- Misses       1760     1763       +3     
  Partials      294      294              

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