feat: run book uploads in a background tray

One request per book instead of one for everything, queued in state above the
dialog so closing it no longer cancels the import. A docked tray reports each
book and offers a retry; it clears itself after a clean run, stays put if
anything failed, and holds while hovered.

Also fixes the dialog overflowing on long filenames — Dialog.Content is a grid
and its body needed min-w-0 to shrink below the content's intrinsic width.

frontend/src/routes/(root)/+layout.svelte

@@ -2,12 +2,14 @@
 	import { listBookshelves } from '$lib/api';
 	import AppSidebar from '$lib/components/layout/app-sidebar.svelte';
 	import SiteHeader from '$lib/components/layout/site-header.svelte';
+	import UploadTray from '$lib/components/layout/upload-tray.svelte';
 	import { Loading } from '$lib/components/ui/command';
 	import * as Sidebar from '$lib/components/ui/sidebar/index.js';
 	import type { Library, PaginatedResponse } from '$lib/schema';
 	import { setBookOperationsState } from '$lib/state/bookOperations.svelte';
 	import { setBookshelfState } from '$lib/state/bookshelf.svelte';
 	import { setLibraryState } from '$lib/state/library.svelte.js';
+	import { setUploadQueueState } from '$lib/state/upload-queue.svelte';
 	import { setThemeState } from '$lib/theme/theme.svelte';
 	import type { ThemeConfig } from '$lib/theme/presets';
 
@@ -30,6 +32,10 @@
 	const bookOps = setBookOperationsState(libraryState.activeLibrary!.id);
 	const theme = setThemeState(untrack(() => data.theme));
 
+	// Set here rather than beside the upload dialog so a running import survives
+	// the dialog closing and any navigation within the app shell.
+	setUploadQueueState();
+
 	// Inline custom properties live on :root and so are mode-blind. When the
 	// light/dark switch flips, rewrite them for the mode now showing.
 	$effect(() => {
@@ -52,3 +58,7 @@
 		</div>
 	</Sidebar.Provider>
 </div>
+
+<!-- Outside the sidebar shell: an import keeps running while you browse, so the
+     tray must not sit anywhere a page swap can take away. -->
+<UploadTray />