fix: resolve all 5 dependabot alerts (undici) and upgrade to node24

- Add npm overrides to force undici@^6.24.1 (fixes all 5 CVEs)
- Update action.yml from node20 to node24
- 0 vulnerabilities in npm audit

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tidy-dev

action.yml

@@ -36,5 +36,5 @@ outputs:
     description: 'JSON array of entries flagged for human review'
 
 runs:
-  using: 'node20'
+  using: 'node24'
   main: 'dist/index.js'