feat: evidence composition — compile-time reference resolution for evidence sub-rules

An evidence may now reference another derived evidence as a sub-rule
(WHEN can_read(user, doc) where can_read is itself an evidence). Resolution
is a compile-time linker pass: after every evidence config is generated, each
direct reference to an evidence is inlined with that evidence's own (resolved)
config, so the engine evaluates a fully-resolved, acyclic config tree.

- resolveEvidenceReferences(): post-generation pass over evidence configs,
  recursing into logical/defeasible containers (when/unless/never/always/
  requires/union/intersection), always.direct nests, and comparator operands.
- Forward references resolve (all configs exist before the pass runs).
- Cycles and self-references are compile-time errors.
- _subjectAsObject scoping is preserved through inlining.
- dependsOn is recomputed after resolution, so partial-graph requirements
  reach transitively through composed evidence.
- buildDirectRule/buildPredicateRule now apply subject-scoping to top-level
  PredicateCall evidence bodies (latent gap, previously missed).
- validation: reject relation names shared across facts/sources/evidence/
  measures (a collision silently overwrote configs and read as a false cycle).

Tests: EvidenceComposition (9), DSLRuntime transitive requiredFacts, oracle
campaign composition construct, illegal-mutations cycle + cross-kind cases.

tests/rigor/dsl-illegal-mutations.test.js

@@ -81,6 +81,21 @@ const MUTATIONS = {
     desc: 'evidence declared with mismatched parameter arity',
     mustFail: true,
     apply: () => VALID_DSL.replace('evidence can_read(user: Employee, doc: Doc) { owns(user, doc) }', 'evidence can_read(user: Employee) { owns(user, doc) }')
+  },
+  cyclic_evidence_ref: {
+    desc: 'two evidences referencing each other (cycle)',
+    mustFail: true,
+    apply: () => VALID_DSL + `
+  evidence can_cyc_a(user: Employee, doc: Doc) { can_cyc_b(user, doc) }
+  evidence can_cyc_b(user: Employee, doc: Doc) { can_cyc_a(user, doc) }`
+  },
+  cross_kind_collision: {
+    desc: 'fact and evidence sharing a relation name',
+    mustFail: true,
+    apply: () => VALID_DSL.replace(
+      'evidence can_read(user: Employee, doc: Doc) { owns(user, doc) }',
+      'fact can_read(user: Employee, doc: Doc)\n  evidence can_read(user: Employee, doc: Doc) { owns(user, doc) }'
+    )
   }
 };