Release httpsig v1.6.0

Minor bump for the additive returnSent fetch option.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: rohanharikr

httpsig/package.json

@@ -1,6 +1,6 @@
 {
     "name": "@hellocoop/httpsig",
-    "version": "1.5.1",
+    "version": "1.6.0",
     "description": "HTTP Message Signatures (RFC 9421) with Signature-Key header support",
     "repository": {
         "type": "git",