chore: format the tree and clear ruff's findings

Applies ruff format, ruff check --fix and prettier, so CI can gate on all three.
The surviving unused imports were all re-exports in __init__.py, now covered by a
per-file ignore; the pdf.js viewer and the generated openapi types join the
vendored code that eslint and prettier already skip.

frontend/src/lib/components/view/book-actions-menu.svelte

@@ -49,7 +49,8 @@
 					Read
 				</DropdownMenu.Item>
 				<DropdownMenu.Item
-					onclick={() => bookOps.downloadBookFile(book.id, book.files[0].id, book.files[0].filename)}
+					onclick={() =>
+						bookOps.downloadBookFile(book.id, book.files[0].id, book.files[0].filename)}
 				>
 					<Download class="size-4" />
 					Download