chore: wire vendored foliate-js into the build

$foliate is a Vite-only alias, deliberately absent from kit.alias and
tsconfig paths: TypeScript cannot resolve it, so the ambient declaration in
src/lib/reader/foliate.d.ts is the only candidate and svelte-check never
walks the ~11k lines of untyped vendored JS. The generated tsconfig includes
src/**/*.js and checkJs is on, so src/lib/vendor is excluded as well —
`exclude` replaces rather than merges, hence the repeated service-worker
entries.

optimizeDeps.include for construct-style-sheets-polyfill: it sits behind a
dynamic import in fixed-layout.js, so Vite would otherwise discover it
mid-session and force a page reload on the first fixed-layout EPUB.

Verified with a temporary import that the graph resolves: view.js and
paginator.js are emitted as chunks, and the bundled pdf.js is our stub
rather than upstream's bare `import '@pdfjs/pdf.min.mjs'`.

frontend/vite.config.ts

@@ -1,7 +1,23 @@
 import tailwindcss from '@tailwindcss/vite';
 import { sveltekit } from '@sveltejs/kit/vite';
 import { defineConfig } from 'vite';
+import { fileURLToPath } from 'node:url';
 
 export default defineConfig({
-	plugins: [tailwindcss(), sveltekit()]
+	plugins: [tailwindcss(), sveltekit()],
+	resolve: {
+		alias: {
+			// Deliberately a Vite-only alias, and deliberately not in kit.alias or
+			// tsconfig paths. TypeScript cannot resolve `$foliate/*`, so the ambient
+			// declaration in src/lib/reader/foliate.d.ts is the only candidate and
+			// svelte-check never walks the ~11k lines of untyped vendored JS.
+			$foliate: fileURLToPath(new URL('./src/lib/vendor/foliate-js', import.meta.url))
+		}
+	},
+	optimizeDeps: {
+		// Behind a dynamic import in foliate's fixed-layout.js, so Vite would
+		// otherwise discover it mid-session and force a full page reload the first
+		// time someone opens a fixed-layout EPUB.
+		include: ['construct-style-sheets-polyfill']
+	}
 });