chore(release): 6.0.0 — Voyage never starts Claude Code

Valgt 6.0.0 (major) because the change is incompatible for a 5.11.1 user:
/trekexecute multi-session no longer finishes in one call, /trekplan
--decompose no longer writes launch.sh, and the per-session turn/budget
environment variables no longer apply. Version synced in plugin.json,
package.json, package-lock.json (both fields), the README badge and the
CHANGELOG heading.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "voyage",
-  "version": "5.11.1",
+  "version": "6.0.0",
   "private": true,
   "description": "Voyage — brief, research, plan, execute, review, continue. Contract-driven Claude Code pipeline. /trekbrief, /trekplan, and /trekreview each end by building a self-contained operator-annotation HTML (scripts/annotate.mjs, pencil-toggle annotation pattern): select text or click any heading/paragraph/list-item, pick intent (Fiks/Endre/Spørsmål), write comment, copy structured prompt, paste back, Claude revises the .md.",
   "type": "module",