release: v1.18.0

[sonukapoor]

Bumps version to v1.18.0 and updates CHANGELOG and site version badge.

Added

• Targeted retry and offline hints for OSV 429 and 5xx error responses
• Lockfile-refresh fix commands for pnpm, yarn, and bun when the parent's declared range already covers the fixed transitive dependency version

Fixed

• Package manager hint added to --fix command failure errors

Changed

• Workspace-scoped lockfile-refresh commands for pnpm, yarn, and bun; fix-plan sections for lockfile-refresh targets separated from direct-fix targets; fix coverage count added to terminal and HTML output; "within current range" label renamed to "lockfile refresh" with rewritten context strings
• Unified EXCLUDED_DIRS constant for --usage source scanning
• Extracted formatAdvisoryDbFreshness, relativeAge, CLI flag validation, formatAdvisorySourceLine, countBySeverity, package.json helpers, and magic number constants into dedicated modules

Validation

• npm test
• npm run build