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/tsconfig.json

@@ -10,7 +10,21 @@
 		"sourceMap": true,
 		"strict": true,
 		"moduleResolution": "bundler"
-	}
+	},
+	// `exclude` replaces the generated list rather than merging with it, so the
+	// service-worker entries from .svelte-kit/tsconfig.json are repeated here.
+	// src/lib/vendor is added: it is vendored third-party JS and checkJs is on,
+	// so without this svelte-check reports thousands of errors from foliate-js.
+	"exclude": [
+		"node_modules/**",
+		"src/service-worker.js",
+		"src/service-worker/**/*.js",
+		"src/service-worker.ts",
+		"src/service-worker/**/*.ts",
+		"src/service-worker.d.ts",
+		"src/service-worker/**/*.d.ts",
+		"src/lib/vendor/**"
+	]
 	// Path aliases are handled by https://svelte.dev/docs/kit/configuration#alias
 	// except $lib which is handled by https://svelte.dev/docs/kit/configuration#files
 	//