perf: ask for previews the size they are shown at

[skjnldsv]

Every image preview was requested at the full size of the display, in device pixels, whatever space it was actually shown in:

+ `&x=${Math.floor(screen.width * devicePixelRatio)}`
+ `&y=${Math.floor(screen.height * devicePixelRatio)}`

On a 4K HiDPI client that is 7680x4320 asked of the preview endpoint for a photo shown beside an open sidebar, and the server renders and caches one preview per size asked for. The handler knows the room it has, so it asks for that, capped at what the display can show and rounded up to a multiple of 256 so a window a few pixels wider reuses the preview that already exists instead of starting a new render.

Three smaller ones of the same kind:

• the one @nextcloud/vue barrel import is now the component itself, so a consumer's bundler is not handed the whole library for a loading spinner: from "@nextcloud/vue/components/NcLoadingIcon" in dist/chunks/Images.mjs
• the svg sanitizer loads from the branch that sanitizes, so it no longer rides along with every image: import("dompurify") is the only reference left in that chunk
• the plyr controls take their listeners once rather than on every update, which a resize triggers many times over (the test counts 4 and 6 addEventListener calls across two updates before, 0 after)
• a folder listing is dropped when the viewer is asked for something else, instead of running to completion for a folder nobody is looking at any more

Six tests fail without the changes. The two source-level guards in __tests__/imports.spec.ts are there because neither import shows up in a unit test, only in the built chunk.

Left out on purpose: caching the sorting config across openFolder calls, which would save one small request per folder open at the cost of showing a stale order after the user changes their sorting, with no event to invalidate it on.

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

[codecov]

Codecov Report

❌ Patch coverage is 86.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.75%. Comparing base (abbbb9c) to head (3e87a70).

Files with missing lines	Patch %	Lines
lib/views/Viewer.vue	50.00%	5 Missing ⚠️
lib/components/Videos.vue	0.00%	1 Missing ⚠️
lib/utils/previewUtils.ts	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
+ Coverage   84.33%   84.75%   +0.42%     
==========================================
  Files          36       36              
  Lines        2432     2467      +35     
  Branches      486      499      +13     
==========================================
+ Hits         2051     2091      +40     
+ Misses        377      372       -5     
  Partials        4        4              

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