chore(release): config-audit v5.7.0 — optimization lens + living knowledge layer

Release-cut for v5.7 Fase 1 (Chunks 1/2a/2b/3):
- best-practices register (knowledge/best-practices.json)
- CA-OPT-001 deterministic optimization-lens scanner (count 14→15)
- /config-audit optimize + optimization-lens-agent (opus, agents 6→7)
- /config-audit knowledge-refresh (commands 19→20)

plugin.json 5.6.0→5.7.0, README version badge + version-history row,
CHANGELOG [5.7.0] entry. Count badges already track filesystem
(self-audit --check-readme: passed). Suite 1091 green (hermetic HOME),
self-audit A/A (config 94, plugin 100).

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

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "config-audit",
   "description": "Multi-agent workflow for analyzing, reporting, and optimizing Claude Code configuration across your entire machine",
-  "version": "5.6.0",
+  "version": "5.7.0",
   "author": {
     "name": "Kjell Tore Guttormsen"
   },