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/rigor/dsl-mutation-parity.test.js

@@ -17,7 +17,7 @@ import { describe, it } from 'node:test';
 import assert from 'node:assert/strict';
 import { rigor } from '@rigor/core';
 import { Arbiter } from '../../src/index.js';
-import { DSLCompiler } from '../../src/ast/DSLCompiler.js';
+import { DSLCompiler } from '@arbiter/evidence-dsl/DSLCompiler';
 
 const EPS = 1e-9;
 const POS = [0, 0.25, 0.5, 0.75, 1];