datalog: rose-ash demo programs (Phase 10 syntactic, 153/153)

New lib/datalog/demo.sx with three Datalog-as-query-language demos
over synthetic rose-ash data:

  Federation: (mutual A B), (reachable A B), (foaf A C) over a
              follows graph.
  Content:    (post-likes P N) via count aggregation, (popular P)
              for likes >= 3, (interesting Me P) joining follows
              + authored + popular.
  Permissions: (in-group A G) over transitive subgroup chains,
              (can-access A R).

10 tests run each program against in-memory EDB tuples loaded via
dl-program-data.

Wiring to PostgreSQL and exposing as a service endpoint (/internal
/datalog) is out of scope for this loop — both would require
edits outside lib/datalog/. Programs above document the EDB shape
a real loader would populate.

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 143,
+  "total_passed": 153,
   "total_failed": 0,
-  "total": 143,
+  "total": 153,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -12,7 +12,8 @@
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":10,"failed":0,"total":10},
-    {"name":"api","passed":9,"failed":0,"total":9}
+    {"name":"api","passed":9,"failed":0,"total":9},
+    {"name":"demo","passed":10,"failed":0,"total":10}
   ],
-  "generated": "2026-05-08T08:33:54+00:00"
+  "generated": "2026-05-08T08:45:37+00:00"
 }