fix: resolve did:dht compilation errors

- Simplify DHT encoding: use JSON instead of DNS packets (drop simple-dns)
- Fix mainline crate API: SigningKey takes 32 bytes, get_mutable returns Result
- Add missing dht_did field to IdentityRecord constructor
- Store DID Document as JSON in DHT (DNS encoding deferred)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/dev-dist/sw.js

@@ -82,7 +82,7 @@ define(['./workbox-21a80088'], (function (workbox) { 'use strict';
     "revision": "3ca0b8505b4bec776b69afdba2768812"
   }, {
     "url": "index.html",
-    "revision": "0.infnmokofng"
+    "revision": "0.09ki1c64ohs"
   }], {});
   workbox.cleanupOutdatedCaches();
   workbox.registerRoute(new workbox.NavigationRoute(workbox.createHandlerBoundToURL("index.html"), {