client/web: use grants on web UI frontend

Starts using peer capabilities to restrict the management client
on a per-view basis. This change also includes a bulky cleanup
of the login-toggle.tsx file, which was getting pretty unwieldy
in its previous form.

Updates tailscale/corp#16695

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

client/web/src/utils/util.ts

@@ -49,3 +49,10 @@ export function isPromise<T = unknown>(val: unknown): val is Promise<T> {
   }
   return typeof val === "object" && "then" in val
 }
+
+/**
+ * isHTTPS reports whether the current page is loaded over HTTPS.
+ */
+export function isHTTPS() {
+  return window.location.protocol === "https:"
+}