evidence-dsl: extract Evidence DSL v2 compiler from @arbiter/core

The Evidence DSL (ADR-000) is a thin declarative layer that compiles to
engine rule types. It has zero runtime coupling to the core engine
(DSLCompiler takes an arbiter as a duck-typed argument; the only shared
code was the ip-utils helpers, now local). Extracting it into its own
package keeps the core artifact free of the DSL surface.

- @arbiter/evidence-dsl depends on @arbiter/core (config formats are the
  compilation target)
- deep-path exports for the compiler, parser, generator, validation,
  and built-in functions (the surface the core's DSL tests consume)
- tests moved alongside; generate-parser script + peggy devDep local
- CI: test on push, publish on v* tags

.gitignore

@@ -0,0 +1,2 @@
+node_modules/
+*.log