Prepare 2.0.0-beta.9

[skjnldsv]

Four pull requests since beta.8: the slideshow option (#39), the encryption flag on handlers (#38), the documentation build (#40) and the dependency update (#41).

Two of them change what a consumer has to do. @nextcloud/vue 9.13.0 is now the minimum, because startSlideshow drives NcModal's v-model:slideshow-running and below that version the option silently does nothing. And supportsEndToEndEncryption is new on IHandler: absent means the handler is not offered end-to-end encrypted files, which is the safe default but will change what a third-party handler sees the moment it upgrades.

The editor bump is the other thing worth reading in the entry. An edited JPEG comes back at 46.0 dB PSNR instead of 38.1, and opening a 12 Mpx photo on a phone-class CPU went from 6.1 s to 0.9 s.

Lint, typecheck, 323 unit tests, 28 e2e across both browsers, the build and the 10 kB size budget all pass on this branch.

👾 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 87.99%. Comparing base (b1638a1) to head (daa594c).

Additional details and impacted files

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##             main      #42   +/-   ##
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  Coverage   87.99%   87.99%           
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  Files          36       36           
  Lines        2507     2507           
  Branches      524      524           
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  Hits         2206     2206           
  Misses        297      297           
  Partials        4        4           

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