Adds the canonical Phase 10 example from the plan: "Posts about
cooking by people I follow (transitively)." dl-demo-cooking-rules
defines reach over the follow graph (recursive transitive closure)
and cooking-post-by-network joining reach + authored + (tagged P
cooking). 3 new demo tests cover transitive network, direct-only
follow, and empty-network cases.
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.
