refactor: extract Evidence DSL to @arbiter/evidence-dsl package

The Evidence DSL (ADR-000) compiles a natural DSL into core rule
configurations — it is a separate concern from the engine. The AST had
zero runtime coupling to the core (DSLCompiler takes the arbiter as a
duck-typed argument; ip-utils were the only shared code, now local to
the DSL package). This extraction removes the DSL surface from the core
artifact entirely:

- src/ast/ (748K, ~60 files) moved to @arbiter/evidence-dsl@1.0.0
- ip-utils moved with it (only the DSL consumed them)
- generate-parser script + peggy devDep moved to the DSL package
- the 8 DSL-consuming tests now import from @arbiter/evidence-dsl
  (deep-path exports: DSLCompiler, parser/*, generator/*, validation/*,
  interpreter/*)
- package.json gains the devDependency, drops build:ast/generate:parser

Tarball: AST-free. Rigor 251/251, full suite 838/776/0.

package.json

@@ -32,8 +32,6 @@
     "test:property": "node --test --test-force-exit \"tests/property-based/**/*.test.js\"",
     "test:integration": "node --test --test-force-exit \"tests/integration/*.js\"",
     "test:perf": "RUN_PERF_TESTS=1 node --test --test-force-exit tests/engine/core-performance-targets.test.js",
-    "generate:parser": "node scripts/generate-parser.js",
-    "build:ast": "npm run generate:parser",
     "benchmark": "node --expose-gc scripts/benchmark.js",
     "benchmark:core": "node benchmarks/core-performance-benchmark.js",
     "benchmark:batch": "node benchmarks/batch-size-analysis.js",
@@ -69,6 +67,6 @@
     "@rigor/core": "*",
     "@tenere/benchmark-lib": "^2.0.1",
     "fast-check": "^4.5.3",
-    "peggy": "^5.0.6"
+    "@arbiter/evidence-dsl": "^1.0.0"
   }
 }