feat: DSLRuntime schema introspection, per-relation providers, retrieval loop

The higher-order DSL+Core wrapper now covers the full contract the DSL
informs, beyond the typed mutations already present:

- getSchema(): serializable introspection of the compiled type system —
  entity types/fields, facts (params + injectable flag), evidence (with
  transitive dependsOn), and registered providers. relationNames() lists all
  declared relations. (The DSL's type system was always present; this exposes
  it programmatically.)
- registerFact(relation, fn) / unregisterFact / registeredFacts: per-relation
  async providers that retrieve missing partial-graph edges; per-check
  factProviders merge OVER registered ones.
- Bounded fixed-point provider retrieval loop (maxProviderRounds): each round
  invokes providers for required facts whose edges are not yet injected. A
  provider may return edges for relations other than its own — those satisfy
  the other required facts and can unblock later rounds.
- check() now type-validates FACT relations too (not just evidence); edge
  normalization preserves a provider edge's own relation name.
- removeNode / removeRelation passthroughs; require() throws on denial for
  middleware.
- Field typing extended to the DSL's full value-type universe
  (timestamp/duration accept number or string; object/any accept anything).

Tests: DSLRuntimeExt (schema, registration, merge, fixed-point, require,
removal, fact-check validation, timestamp typing).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@arbiter/evidence-dsl",
-  "version": "1.4.0",
+  "version": "1.5.0",
   "description": "Evidence DSL v2 compiler: translates the natural Evidence DSL (ADR-000) into @arbiter/core relation configurations.",
   "license": "ISC",
   "type": "module",