fix: proto-get case-insensitive keyword lookup

proto-get was using getf which does eq comparison, so :EXPLANATION
from the LLM response didn't match :explanation in the policy gate.
Now iterates the plist and compares uppercased strings.

lisp/core-communication.lisp

@@ -1,8 +1,12 @@
 (in-package :passepartout)
 
 (defun proto-get (plist key)
-  "Look up KEY in PLIST with keyword normalization."
-  (getf plist (if (keywordp key) key (intern (string-upcase (string key)) :keyword))))
+  "Look up KEY in PLIST with case-insensitive keyword normalization."
+  (let ((key-upcase (string-upcase (string key))))
+    (loop for (k v) on plist by #'cddr
+          when (and (keywordp k)
+                    (string-equal (string k) key-upcase))
+            do (return v))))
 
 (defvar *actuator-registry* (make-hash-table :test 'equalp)
   "Global registry mapping target keywords to their physical actuator functions.")