chore(deps): fix yarn audit vulnerabilities (#4404)

Runs `yarn audit-fix` to patch transitive dependency vulnerabilities.
Upgrades: ajv@6.14.0, brace-expansion@1.1.12, form-data@4.0.4,
js-yaml@3.14.2, minimatch@3.1.4, webpack@5.104.0.

Reduces vulnerabilities from 73 to 12. Remaining 12 are blocked by
upstream packages (@flarum/jest-config, flarum-webpack-config) pinning
older versions — all dev-tool only, nothing shipped to users.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: imorland