datalog: Phase 6 adornments + SIPS analysis (194/194)

New lib/datalog/magic.sx — first piece of magic-sets:

  dl-adorn-arg arg bound          → "b" or "f"
  dl-adorn-args args bound        → adornment string
  dl-adorn-goal goal              → adornment under empty bound set
  dl-adorn-lit lit bound          → adornment of any literal
  dl-vars-bound-by-lit lit bound  → free vars this lit will bind
  dl-init-head-bound head adn     → bound set seeded from head adornment
  dl-rule-sips rule head-adn      → ({:lit :adornment} ...) per body lit

SIPS walks left-to-right tracking the bound set; recognises `is` and
aggregate result-vars as new binders, lets comparisons and negation
pass through with computed adornments.

Inspection-only — saturator doesn't yet consume these. Lays
groundwork for a future magic-sets transformation.

10 new tests cover pure adornment, SIPS over a chain rule,
head-fully-bound rules, comparisons, and `is`. Total 194/194.

lib/datalog/conformance.conf

@@ -13,6 +13,7 @@ PRELOADS=(
   lib/datalog/strata.sx
   lib/datalog/eval.sx
   lib/datalog/api.sx
+  lib/datalog/magic.sx
   lib/datalog/demo.sx
 )
 
@@ -26,5 +27,6 @@ SUITES=(
   "negation:lib/datalog/tests/negation.sx:(dl-negation-tests-run!)"
   "aggregates:lib/datalog/tests/aggregates.sx:(dl-aggregates-tests-run!)"
   "api:lib/datalog/tests/api.sx:(dl-api-tests-run!)"
+  "magic:lib/datalog/tests/magic.sx:(dl-magic-tests-run!)"
   "demo:lib/datalog/tests/demo.sx:(dl-demo-tests-run!)"
 )