feat(schema): add pi-schema, JSON Schema builders and validation without eval

@earendil-works/pi-schema compiles JSON Schema (drafts 2020-12 and 7) once into
plain closures: no eval or new Function, so it runs under a strict CSP. It
passes 2,222 of the 2,223 core tests of the official JSON-Schema-Test-Suite,
checks Chord-style argument schemas within 1.2x of TypeBox's JIT, and keeps
3,200 compiled schemas in 7.9 MB (TypeBox: 54.7 MB).

- compile(schema, options) returns a Validator: check() is the boolean check
  (a type guard for builder schemas), errors() reports each failure with a
  JSON Pointer path, missing and unknown fields at the field.
- Builders (str, int, obj, opt, union, ...) return plain JSON Schema typed with
  the values it accepts (Static<typeof schema>).
- Formats are an optional entry point (./formats), adapted from TypeBox (MIT).
- Tests run the vendored suite (drafts 2020-12 and 7, with optional and format
  tests); npm run bench compares conformance, speed, setup cost, memory and
  bundle size with TypeBox, @cfworker/json-schema and omptype.

tsconfig.json

@@ -34,6 +34,8 @@
 			"@earendil-works/pi-codemode/portable": ["./packages/codemode/src/portable.ts"],
 			"@earendil-works/pi-codemode/source": ["./packages/codemode/src/source.ts"],
 			"@earendil-works/pi-codemode/worker": ["./packages/codemode/src/runtime/worker.ts"],
+			"@earendil-works/pi-schema": ["./packages/schema/src/index.ts"],
+			"@earendil-works/pi-schema/formats": ["./packages/schema/src/formats/index.ts"],
 			"@earendil-works/pi-mcp": ["./packages/mcp/src/index.ts"],
 			"@earendil-works/pi-mcp/oauth": ["./packages/mcp/src/oauth/index.ts"],
 			"@earendil-works/pi-mcp/testing": ["./packages/mcp/src/testing/index.ts"],