Add list view + per-grouping persistence for the audiobooks library

[kevinheneveld]

Summary

Two related changes to the audiobooks library's grouped views, combined into one PR (was previously split across #585 and #590; #590 is being closed in favor of this).

1. List view for grouped authors and series. The audiobooks toolbar exposes a list/grid view toggle, but the grouped views (?group=authors, ?group=series) only had a grid template. Toggling list mode while grouped was silently a no-op. This PR adds a parallel list rendering for grouped collections: one row per collection (cover thumb, collection name, book count). Clicking a row navigates to the collection page, matching the grid-card behavior.

2. Per-grouping persistence of the view mode. Previously the load-from-storage was nested inside an if (scrollContainer.value) block that only runs for the Books grouping — so switching to list mode while grouped by Author or Series, then navigating away, would silently revert to grid. This switches to three per-grouping keys (listenarr.viewMode.books, .authors, .series) and reads the relevant one unconditionally on mount + whenever groupBy changes. A one-time migration seeds all three keys from the legacy listenarr.viewMode value so existing users keep their preference.

Implementation notes

• Template change is localized to the grouped-view block in fe/src/views/library/AudiobooksView.vue. The existing grid is wrapped in v-else; new v-if=\"viewMode === 'list'\" branch above it.
• CSS reuses the existing .audiobooks-list / .audiobook-list-item patterns; collection rows have their own three-column grid template (cover / name / count) since they don't carry status badges or per-item actions.
• Persistence watch moved out from inside the scrollContainer guard to a top-level watch, so it fires regardless of grouping. Removed the now-unused `stopPersistViewModeWatch` cleanup handle.
• Initial viewMode is set inline at declaration: `ref<...>(loadViewModeFor(groupBy.value))`.
• Migration is additive — the legacy key is never deleted, just no longer read once the per-grouping keys exist.
• `viewMode` and `toggleViewMode` are exposed via `defineExpose` so tests can drive the view deterministically.

Test plan

• `cd fe && npm run test:unit` — 14 / 14 AudiobooksView tests passing (4 new: list-view rendering for authors + series, per-grouping persistence, legacy migration)
• `cd fe && npm run type-check` — clean
• Rebased onto canary tip (post-1.0.1); resolved one spec-file conflict (type-field adjacency) and re-ported the persistence change onto the new initializeVirtualScroller refactor

Closes #595
Supersedes #590

[T4g1]

Small note regarding the issue linked to this: Is there a particular reason why you created it on the fork instead of here ? It might be better to open them here instead if you expect feedback on those (or perhaps there is a way to see forked repository issues from here ?)

[kevinheneveld]

Good point. My workflow tracks issues on the fork as a working backlog, but you're right that anything expecting upstream feedback belongs here. I'll re-open this one on Listenarrs/Listenarr and relink it.

[kevinheneveld]

Re-filed the linked issue here: #595 (was kevinheneveld#1). Will update the PR body to point at the new one.

[therobbiedavis]

Thanks for taking care of this; it was actually on my list of todo's eventually. I left a couple of inline comments around the new grouped-list image path: the fallback argument is currently not a real image URL, and the author list rows do not participate in the existing author-cover lookup flow used by grid cards.

[therobbiedavis]

getProtectedImageSrc() treats its second argument as the actual fallback image URL, not as an image/cache key. With the current value, coverless author/series rows get a src like authors-list:Author A or series-list:Series 1 until the image error handler replaces it. Could this pass getPlaceholderUrl() instead?

[therobbiedavis]

This new author list path bypasses the existing author-cover lookup behavior. Grid author cards call into ensureAuthorCover() through handleAuthorImageError() and the observeAuthorCards() marker selector at AudiobooksView.vue:1519, but these list rows only use the generic handleImageError and do not render a data-author-name target. For authors without authorAsins, list mode will stay on the placeholder instead of fetching the lookup cover.

I’d avoid fixing this only by swapping @error to handleAuthorImageError: once my previous comment changes the fallback to a valid placeholder, no error fires for missing covers, so lookup still won’t happen. A safer fix would make list author rows participate in the same lazy observer path, and add a test where an author has no authorAsins but apiService.getAuthorLookup() returns a cover.