feat(engine): complete deterministic LDL compiler facade

[Dencyuman]

Summary

• add the transport-neutral Engine.Compile facade over the complete LDL compiler pipeline
• validate closed Project and Pack inputs, resolved dependency metadata, assets, resource limits, and cancellation atomically
• publish complete defensive snapshots containing normalized artifacts, indexes, hashes, recipes, search documents, diagnostics, and authoring classifications
• add deterministic, race-safe, fuzz, large-graph, package-boundary, and conformance coverage

Guarantees

• semantic rejection publishes diagnostics only, with no partial artifact
• cancellation, resource exhaustion, and invariant failures return typed errors with an empty result
• repeated and permuted equivalent inputs produce identical semantic output
• the compiler performs no filesystem, network, credential, state, clock, framework, or TypeScript access
• raster resources are bounded before full image decoding

Validation

• NODE_VERSION=24.18.0 /Users/dencyu/.nvm/nvm-exec make ci
• overall coverage: 95.7%
• internal/engine coverage: 96.0%
• patch coverage: 95.9%
• race, conformance, fuzz smoke, license, vulnerability, audit, build, and packaged binary checks passed

Closes #18

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