chore(voyage): release v5.6.0 — /trekexecute loop hardening

Bump plugin.json, package.json, package-lock.json, and the README badge
to 5.6.0; prepend CHANGELOG v5.6.0 entry + README "What's new" block for
the S38 loop-hardening work (machine-verifiable completion gate, bounded
recovery cap hierarchy + global budget, iterations_remaining signal,
fan-out hedge harmonization).

Additive — no breaking change. Canonical node --test stays 756 (0 fail);
version-consistency test green across all five version refs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "voyage",
-  "version": "5.5.0",
+  "version": "5.6.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "voyage",
-      "version": "5.5.0",
+      "version": "5.6.0",
       "license": "MIT",
       "engines": {
         "node": ">=18"