mod: Ext 3 — human-readable proof explanation (mod/explain), 164/164

mod/explain renders a decision's proof tree into legible text: action + rule,
evidence line, and each derivation goal with [proved]/[unproved] and the
unification bindings that satisfied it (e.g. {B=ann, N=3, S=dave}). Pure SX over
the Phase-2 proof data — the audit trail's 'why' made readable. +10 tests.

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

lib/mod/scoreboard.json

@@ -1,14 +1,14 @@
 {
   "lang": "mod",
-  "total_passed": 154,
+  "total_passed": 164,
   "total_failed": 0,
-  "total": 154,
+  "total": 164,
   "suites": [
     {"name":"decide","passed":31,"failed":0,"total":31},
     {"name":"audit","passed":29,"failed":0,"total":29},
     {"name":"escalation","passed":46,"failed":0,"total":46},
     {"name":"fed","passed":26,"failed":0,"total":26},
-    {"name":"extensions","passed":22,"failed":0,"total":22}
+    {"name":"extensions","passed":32,"failed":0,"total":32}
   ],
-  "generated": "2026-06-06T18:02:25+00:00"
+  "generated": "2026-06-06T18:05:54+00:00"
 }