Modernize ResGraph architecture and runtime safety

[zth]

Summary

• harden GraphQL execution, DataLoader, Yoga bindings, schema validation, artifact writes, LSP behavior, packaging, and release checks
• extract the native generator into a wrapped engine library with an opaque reusable generation context
• batch schemas by canonical compiler root through a versioned private protocol, sharing CMT/module summaries while preserving aligned per-schema results and failure isolation
• add native/runtime/package-consumer/multi-schema coverage, a published config JSON Schema, architecture documentation, and the staged modernization plan

Architectural scope

This implements the safety/correctness milestone and the shared multi-schema engine seam without attempting an unsafe wholesale canonical-IR rewrite. The published plan keeps the canonical IR, complete emitter transaction, compact editor DTO, and measurement-gated hot-path work behind their stated differential-compatibility and performance gates.

Verification

• native dune build @fmt, dune runtest, and native build
• full make -C tests test integration suite
• npm test runtime binding suite
• npm run test:package clean packed-consumer fixture
• root CLI bundle build
• VS Code extension typecheck and bundle
• Docusaurus production build
• workflow YAML, shell syntax, JSON, and git diff --check validation