fix(nip05): add redirect prevention docs and zap field validation

Gap #5: Document NIP-05 spec requirement that /.well-known/nostr.json
MUST NOT return HTTP redirects. The extension already complies (always
returns direct responses), but reverse proxy deployments need awareness.

Gap #7: Log a warning when getLnurlPayInfo() response is missing
allowsNostr or nostrPubkey fields required by NIP-57 for zap support.
This surfaces misconfiguration early instead of silently breaking zaps.

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

src/extensions/nip05/index.ts

@@ -189,6 +189,12 @@ export default class Nip05Extension implements Extension {
    *   "relays": { "<pubkey hex>": ["wss://..."] }
    * }
    */
+  /**
+   * NIP-05 spec: "The /.well-known/nostr.json endpoint MUST NOT return any
+   * HTTP redirects." This extension always returns direct 200/4xx/5xx responses.
+   * Deployment note: ensure reverse proxies do not add 3xx redirects on this path
+   * (e.g. HTTP→HTTPS or trailing-slash redirects).
+   */
   private async handleNostrJson(req: HttpRequest): Promise<HttpResponse> {
     try {
       // Get application ID from request context
@@ -272,6 +278,11 @@ export default class Nip05Extension implements Extension {
         description: `Pay to ${username}`
       })
 
+      // NIP-57: ensure zap support fields are present for wallet compatibility
+      if (!lnurlPayInfo.allowsNostr || !lnurlPayInfo.nostrPubkey) {
+        this.ctx.log('warn', `LNURL-pay response for ${username} missing zap fields (allowsNostr=${lnurlPayInfo.allowsNostr}, nostrPubkey=${!!lnurlPayInfo.nostrPubkey}). Zaps will not work.`)
+      }
+
       return {
         status: 200,
         body: lnurlPayInfo,