chore: prepare 2.0.0-beta.14

[skjnldsv]

Version bump and changelog for 2.0.0-beta.14: the tagName rename (#81), the loading and error feedback (#78, #79, #80), and previews on shares that forbid downloading (#51).

#81 moves the shared registry to handlers_v2, so nextcloud/server has to bump to this release before apps do, or the two copies stop sharing a viewer. That bump is also what the real-server e2e suite (#82) needs to go green again: it runs against server master, which still bundles beta.13.

#77 and #83 are still open; merge them first if they should be in this one, and I'll add them to the changelog.

👾 This pull request was assisted by Claude Code, commits carry an Assisted-by trailer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.17%. Comparing base (9cb0b2e) to head (ff30bbd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #84   +/-   ##
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  Coverage   89.17%   89.17%           
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  Files          39       39           
  Lines        2845     2845           
  Branches      588      588           
=======================================
  Hits         2537     2537           
  Misses        301      301           
  Partials        7        7           

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