fix(spa): Fix relative alias redirects

Missed this in my initial fix, but for subpath hosting support the
redirects are relative, and aliases from deeply nested folders try to
fetch the wrong thing.

For example:
In page a/b/C.md we have a link [[K]], and in page x/y/Z.md we specify
`aliases: K`.
The emitted alias redirect will be x/y/K.html and will redirect to
`../Z.html`.

The emitted html link will point to `x/y/K.html`, which the SPA/popover
will fetch, read `../Z.html` from it, and try to fetch `a/b/Z.html`,
because it'll be relative to where the link is, which is wrong.

So we resolve the relative URL by using the URL constructor and giving
it `x/y/K.html` as the base, so that `../Z.html` will correctly resolve

quartz/components/scripts/util.ts

@@ -41,5 +41,5 @@ export async function fetchCanonical(url: URL): Promise<Response> {
   // to allow the caller to read it if it's was not a redirect
   const text = await res.clone().text()
   const [_, redirect] = text.match(canonicalRegex) ?? []
-  return redirect ? fetch(redirect) : res
+  return redirect ? fetch(`${new URL(redirect, url)}`) : res
 }