Fix npm dependency security advisories

[realDuang]

Summary

• Refresh dev dependency lockfile entries within existing semver ranges.
• Add a pnpm override for Vite 6.4.2 so VitePress resolves to the patched Vite line.
• Resolve local audit findings for vite, esbuild, picomatch, brace-expansion, flatted, minimatch, ajv, diff, and postcss.

Validation

• pnpm audit
• pnpm check
• pnpm test
• pnpm docs:build
• VitePress dev server responded with HTTP 200 locally
• VitePress preview server responded with HTTP 200 locally