fix(js): add typed ChallengeResult interface for PoW worker results

The process() function in fast.ts declared Promise<string> but actually
resolved with the full worker message object { hash, data, difficulty,
nonce }. main.tsx papered over this with `any`. Introduce a shared
ChallengeResult type so the contract between workers, algorithms, and
the main component is enforced by the type checker.

Assisted-by: Claude Opus 4.6 via Claude Code
Signed-off-by: Xe Iaso <me@xeiaso.net>

web/js/main.tsx

@@ -1,6 +1,6 @@
 import { render } from "preact";
 import { useState, useEffect, useRef } from "preact/hooks";
-import algorithms from "./algorithms";
+import algorithms, { ChallengeResult } from "./algorithms";
 
 // from Xeact
 const u = (url: string = "", params: Record<string, any> = {}) => {
@@ -211,7 +211,7 @@ function App({ anubisVersion, basePrefix }: AppProps) {
         }
       },
     )
-      .then((result: any) => {
+      .then((result: ChallengeResult) => {
         const t1 = Date.now();
         const { hash, nonce } = result;