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.

tests/engine/builtin-functions.test.js

@@ -11,7 +11,7 @@ import {
   evaluateBuiltIn,
   getFunctionSignature,
   BUILT_IN_FUNCTIONS
-} from '../../src/ast/interpreter/BuiltInFunctions.js';
+} from '@arbiter/evidence-dsl/interpreter/BuiltInFunctions';
 
 describe('Built-in Functions Registry', () => {
   it('should identify built-in functions', () => {