test(lib): cover safeHref validation

[alan-provable]

Closes #144

Summary

• Consolidates safeHref coverage into table-driven accept/reject cases.
• Covers uppercase HTTPS, root-relative links, hash links, dangerous schemes, protocol-relative URLs, nullish and blank inputs, bare words, missing-colon URLs, colon-at-index-zero inputs, mailto, tel, ftp, and obfuscated schemes.
• Adds a 100 percent per-file Jest coverage threshold for src/lib/url.ts.
• Adds missing imports in src/app/docs/page.tsx so current main can typecheck and lint after the recent docs-page changes.

Validation

• npm run typecheck
• npm run lint
• npx eslint src/lib/url.ts src/lib/__tests__/url.test.ts jest.config.ts
• npx jest src/lib/__tests__/url.test.ts --coverage --collectCoverageFrom=src/lib/url.ts --coverageThreshold='{"./src/lib/url.ts":{"statements":100,"branches":100,"functions":100,"lines":100}}'
  • 25 tests passed.
  • src/lib/url.ts reached 100 percent statements, branches, functions, and lines.
• git diff --check origin/main..HEAD

Known Baseline

• npm test still has 2 unrelated failures in untouched src/components/__tests__/Header.test.tsx; the suite otherwise reports 561 passing tests and 2 skipped tests.