Add node field XSS sanitization

[real-venus]

Summary

Implements XSS protection for dynamic node identifier strings in the VeriNode frontend.

Closes #9

Changes

• Added DOMPurify-based sanitization for node fields:
  • displayName
  • description
  • location
  • contactEmail
  • websiteUrl
• Added SafeText component for safe plain-text rendering.
• Added network node components:
  • NodeCard
  • NodeList
  • NodeDetailPanel
• Integrated sanitized node rendering into /network.
• Added ESLint ban for dangerouslySetInnerHTML.
• Added CSP headers in next.config.ts.
• Added fast-check/Vitest property tests with 500 malicious strings.
• Added Playwright XSS regression test for injected node fields.