chore(voyage): release v5.6.1 — one-line descriptions for reference/dormant agents (~700 tok trim)

Trim the always-loaded token cost of the agent listing Claude Code injects
into every session. The three *-orchestrator reference docs
(planning/research/review) and the dormant synthesis-agent carried
multi-paragraph description: frontmatter (full rationale + CC-2.1.172
history + a usage example) despite never being spawnable from the live
/trek* pipeline; their description is now a single line, with the full
rationale already living — and remaining — in each file's body. ~700
tokens trimmed, no behavior change.

The three orchestrators retain the self-declaration "reference document,
not a spawnable capability" (doc-consistency pin); synthesis-agent retains
its DORMANT / not-wired flag + docs/T1-synthesis-poc-results.md pointer.
Bump plugin.json, package.json, package-lock.json, and the README badge to
5.6.1; prepend CHANGELOG v5.6.1 entry + README What's-new note. Surfaced
via config-audit always-loaded token-audit dogfooding.

Additive — no breaking change, no runtime behavior change. Canonical
node --test: 739 pass, 0 fail (2 skipped); version-consistency + agent
inventory + frontmatter pins green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CrTb8ktf1XZWEVwgz5MTTo

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "voyage",
-  "version": "5.6.0",
+  "version": "5.6.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "voyage",
-      "version": "5.6.0",
+      "version": "5.6.1",
       "license": "MIT",
       "engines": {
         "node": ">=18"