feat: replace the epub reader with foliate-js

Drops epub.js's 1600-location pre-pass and its localStorage cache: foliate
hands back a CFI and an overall fraction on every relocate, so first open no
longer freezes.

Also fixes resuming (pre-resolves the stored CFI, falling back to the stored
percentage rather than silently resetting to page one), progress saving
(missing Content-Type, and no flush on the way out), and arrow keys inside
the book iframe.

frontend/src/routes/(root)/(library)/book/[bookId]/read/epub/[fileId]/+page.svelte

@@ -7,18 +7,15 @@
 	const fileId = page.params.fileId!;
 	const bookId = page.params.bookId!;
 
-	// Streams the file through the proxy so the browser fetches it directly
+	// Fetched by the browser through the proxy, which attaches the auth header
 	const bookUrl = `/api/books/download/${bookId}/${fileId}`;
 </script>
 
-<svelte:head>
-	<title>{data.title} — Chitai</title>
-</svelte:head>
-
 <EpubReader
 	{bookUrl}
 	{bookId}
 	title={data.title}
+	filename={data.filename}
 	initialProgress={data.initialProgress}
 	initialEpubLoc={data.initialEpubLoc}
 />