Clarify RIS support before 1.4.2 release

[dknauss]

Summary

• Clarify that RIS is supported as an export format, not an input/import format.
• Update plugin/package/readme descriptions to avoid overstating RIS input support.
• Add a planning todo for real reference-manager export testing and record the RIS-import out-of-scope decision.
• Add the RIS clarification to the 1.4.2 changelog/readme entry.

Local validation

• composer lint:php
• composer test:php — passes with existing/vendor PHP 8.5 deprecations
• npm run lint:js
• npm run lint:css
• npm run lint:i18n
• npm test -- --runInBand
• npm run build
• composer audit --no-dev
• npm audit --omit=dev --omit=optional

Release note

Local npm run package:release is blocked by DNS resolution to GitHub for Composer source downloads in this sandbox, so this PR should rely on CI's package artifact job as the network-capable package verification before tagging v1.4.2.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.80%. Comparing base (1a5df5b) to head (9e524a6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #65   +/-   ##
=======================================
  Coverage   80.80%   80.80%           
=======================================
  Files          44       44           
  Lines        3084     3084           
  Branches      523      523           
=======================================
  Hits         2492     2492           
  Misses        185      185           
  Partials      407      407           

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