feat: add camelCase API aliases

[rlippmann]

Summary

Add idiomatic camelCase aliases for TypeScript consumers while preserving the snake_case parity API, update Vitest dependencies to a vulnerability-free release, and prepare package version 0.9.0-dev.2.

Why

TypeScript consumers can use camelCase methods and grammar helpers without changing the Python-compatible API or conformance contract.

Scope checklist

• Diff is minimal and scoped to the requested behavior
• Python/spec parity is preserved
• Fixture semantics are respected
• No unrelated refactors
• Relevant validation was run (npm test)

Notes

• Engine aliases: exportJson, importJson, applyDirective
• Grammar aliases: decomposeDirective, getDirectiveMetadata
• Existing snake_case names remain supported.
• No conformance fixtures or provenance were modified.

Validation details:

• npm test: passed (266/266)
• Focused alias/API tests: passed (32/32)
• fast-check: passed (6/6)
• npm run build: passed
• npm audit: 0 vulnerabilities
• npm pack --dry-run: passed