Release v1.6.4 with dependency security fixes

[Sythos]

Summary

• Align package metadata, public version constants, generated bundles, and release documentation on v1.6.4.
• Update the supported security release line to 1.6.x.
• Carry the verified dependency security fixes and Dependabot updates forward into the release candidate.

Validation

• Lint, documentation, format, core, foundation, and property-based tests passed.
• TypeScript and public declaration checks passed.
• Lockfile security guard and tests passed.
• Bundle/version consistency passed.
• npm pack --dry-run produced 478 files with no tests or tooling included.