chore: update STATE.a2ml date to 2026-03-23 (48 backends)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/6a2/STATE.a2ml

@@ -5,7 +5,7 @@
 [metadata]
 project = "echidna"
 version = "1.5.0"
-last-updated = "2026-03-15"
+last-updated = "2026-03-23"
 status = "active"
 
 [project-context]