chore(release): 6.4.0 — plan_version 1.9, the trial-4 findings, session-clean tests, the converging critic loop

Version 6.4.0 in plugin.json, package.json, package-lock.json and the
README badge; the Unreleased CHANGELOG section becomes v6.4.0 with its
title unchanged, and its Doors list (all two-way) unchanged.

Release review over v6.3.1..main (a97efb6..4e28dc5, 82 files, operator
decision 52): WARN, 0 BLOCKER, 4 MAJOR, 6 MINOR, verdict gate exit 0.
Under decision 52 the four MAJOR go to Known issues, no fix round:
ef1633b6 (a dedup merge lets rule A lower a major in the changed text),
38a8ad34 (regression A also reads a mentioned plain path below 1.9),
20b626e2 and c614baad (two fail-closed exit-2 paths in the verdict gate).
Each was reproduced by running the code at HEAD before it was written
here; 38a8ad34 also against v6.3.1.

Between the review and this commit, b794958 (test-only) lets two docs
tests find the section under its release heading; its own quick review
(4e28dc5..b794958) is WARN, 0 BLOCKER, 6 MAJOR, 2 MINOR, all in test
code, verdict gate exit 0.

The session-id entry under Fixed is narrowed to what the suite does: a
test file run on its own still passes the id to a child it starts
without an env (43 such files measured).

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

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "voyage",
   "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 element, pick intent (Fiks/Endre/Spørsmål), write comment, copy structured prompt, paste back, Claude revises the .md.",
-  "version": "6.3.1",
+  "version": "6.4.0",
   "author": {
     "name": "Kjell Tore Guttormsen"
   },