feat: intermediate chain condition steps + _subjectIsObject unary scoping

- _expandChainSteps: a logical/defeasible evidence referenced by a chain step
  is now a condition step ({ rule, conditionStep }) at ANY position. As the
  FINAL step the engine verifies it at (intermediate, object); as an
  INTERMEDIATE step the engine expands it from the current node (rule-based
  reachability: base edges' destinations filtered by the rule's
  defeaters/requirements) and continues traversal from each discovered node.
- buildPredicateRule / buildDirectRule: unary predicate calls whose subject
  entity IS the evidence's object parameter (trusted(other) inside
  peer_trusted(user, other)) are marked _subjectIsObject (was: only subject-var
  calls got _subjectAsObject). Requires @arbiter/core@^1.0.4.

Tests: ChainConditionStep intermediate expansion; oracle campaign gains a
chain_intermediate_condition construct (oracle = min(peer*(1-trusted), read)).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@arbiter/evidence-dsl",
-  "version": "1.5.0",
+  "version": "1.6.0",
   "description": "Evidence DSL v2 compiler: translates the natural Evidence DSL (ADR-000) into @arbiter/core relation configurations.",
   "license": "ISC",
   "type": "module",
@@ -24,7 +24,7 @@
     "generate:parser": "node scripts/generate-parser.js"
   },
   "dependencies": {
-    "@arbiter/core": "^1.0.3"
+    "@arbiter/core": "^1.0.4"
   },
   "devDependencies": {
     "@rigor/core": "^3.1.0",