chore: prepare v0.6.3

[willytop8]

Summary

• bump the package version from 0.6.2 to 0.6.3
• add the 0.6.3 changelog entry for the completion-protocol prompt hardening
• keep completion detection strict; no detector broadening was warranted by the provider evidence

Verification

• npm run release:check
• 249/249 tests passed
• type checks passed in NodeNext and Bundler modes
• mutation, behavior, packed-host, tool-contract, verifier, audit, and pack dry-run gates passed
• npm audit: 0 vulnerabilities

This PR contains only CHANGELOG.md, package.json, and package-lock.json release metadata.