Refactor Nostr settings/connect

* Use NIP-42 auth event instead of short text note
* Verify event ID and signature using the nostr gem instead of custom code

app/javascript/controllers/settings/nostr_pubkey_controller.js

@@ -3,7 +3,12 @@ import { Controller } from "@hotwired/stimulus"
 // Connects to data-controller="settings--nostr-pubkey"
 export default class extends Controller {
   static targets = [ "noExtension", "setPubkey", "pubkeyBech32Input" ]
-  static values  = { userAddress: String, pubkeyHex: String, sharedSecret: String }
+  static values  = {
+    userAddress: String,
+    pubkeyHex: String,
+    site: String,
+    sharedSecret: String
+  }
 
   connect () {
     if (window.nostr) {
@@ -19,11 +24,15 @@ export default class extends Controller {
     this.setPubkeyTarget.disabled = true
 
     try {
+      // Auth based on NIP-42
       const signedEvent = await window.nostr.signEvent({
         created_at: Math.floor(Date.now() / 1000),
-        kind: 1,
-        tags: [],
-        content: `Connect my public key to ${this.userAddressValue} (confirmation ${this.sharedSecretValue})`
+        kind: 22242,
+        tags: [
+          ["site", this.siteValue],
+          ["challenge", this.sharedSecretValue]
+        ],
+        content: ""
       })
 
       const res = await fetch("/settings/set_nostr_pubkey", {