mod: Ext 2 — weighted/aggregate scoring (:score-at-least), 154/154

Report :signals ({:kind :weight}) project to signal(Id, 'kind', weight) facts;
condition (:score-at-least N) compiles to aggregate_all(sum(W), signal(Id,_,W),T),
T >= N. Low-confidence signals accumulate past a threshold via genuine Prolog
arithmetic aggregation. Default policy untouched — proven via custom rule sets.
+8 extension tests.

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

lib/mod/policy.sx

@@ -45,6 +45,7 @@
 ;; (:attr "verified")       → attr(Id, verified)
 ;; (:not <cond>)            → not(<cond>)        (negation as failure)
 ;; (:count-at-least 3)      → report(Id, B, S), report_count(S, N), N >= 3
+;; (:score-at-least 5)      → aggregate_all(sum(W), signal(Id, _, W), T), T >= 5
 
 (define
   mod/cond->goal
@@ -71,6 +72,12 @@
             idterm
             ", B, S), report_count(S, N), N >= "
             (nth c 1)))
+        ((= tag :score-at-least)
+          (str
+            "aggregate_all(sum(W), signal("
+            idterm
+            ", _, W), T), T >= "
+            (nth c 1)))
         (true "true")))))
 
 (define