feat(viewer): start the slideshow on open

[skjnldsv]

nextcloud/viewer master got startSlideshow in nextcloud/viewer@6534fcd5 after this library forked from it, and Photos already passes it from MemoriesView.vue and TimelineView.vue. The library had no way to start the slideshow from outside, and no way for a video to hold it.

open(nodes, file, { startSlideshow: true }) now starts the slideshow, ignored for a single file, and the state resets on close. Handlers get a fourth emit, update:playing: the slideshow pauses while it is true. The video and audio players emit it from the media element's play and pause events, so a playing clip finishes before the slideshow moves on. The old viewer only did this for videos; I wired the audio player too since the same argument holds.

Important

Depends on nextcloud-libraries/nextcloud-vue#8955, which exposes NcModal's slideshow state as v-model:slideshow-running. Until that is released and the @nextcloud/vue requirement bumped here, the option is a no-op at runtime (the modal ignores the unknown prop), and the slideshow.spec.ts e2e run is red on purpose: it drives the real modal and is the only check that can tell.

Covered by component tests: the option, its single-file and unasked cases, following the play / pause button, reset on close, a handler holding and releasing the slideshow, the hold dropping when the file changes, and both players emitting. The component tests stub NcModal, so they pass either way; the e2e spec passed locally with a build of the nextcloud-vue branch swapped into node_modules, and fails against 9.11 / 9.12.

👾 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 87.96%. Comparing base (7735d90) to head (0df8bcb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
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+ Coverage   87.83%   87.96%   +0.12%     
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  Files          36       36              
  Lines        2474     2500      +26     
  Branches      519      522       +3     
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+ Hits         2173     2199      +26     
  Misses        297      297              
  Partials        4        4              

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