Test/safelink inert rendering coverage

[Favourejiro]

closes #365

tighten unit-test coverage for SafeLink's inert rendering and rel/target attribute enforcement across the full
unsafe-scheme matrix.

While extending the tests, the issue's required assertions surfaced two real link-safety gaps that had to be fixed for the assertions to
hold. Both are small, security-positive changes.

Changes

src/components/SafeLink.tsx — enforce safety attributes

Previously {...props} was spread after target/rel, so a caller could override them (e.g. rel="" or target="_self"),
silently defeating tab-nabbing protection. The spread now comes before the enforced attributes, so target="_blank" and
rel="noopener noreferrer" always win while non-conflicting props (e.g. className) still pass through.

src/utils/url.ts — reject userinfo-bearing URLs

normalizeEvidenceUrl accepted URLs like https://trusted.com@evil.com because the protocol was https:. Userinfo
(username/password) is now rejected — it's a common credential/phishing vector that hides the real host.

src/components/__tests__/SafeLink.test.tsx — expanded coverage

• Unsafe-scheme matrix (test.each): javascript:, data:, empty, whitespace-only, missing-scheme, and userinfo-bearing URLs all
  render the inert [Invalid Link] span with the Rejected URL: … title.
• Safe URLs: http/https (incl. query strings) render an <a> with target="_blank" and rel="noopener noreferrer".
• Conflicting-props case: caller-supplied target/rel cannot override the enforced values.
• Prop forwarding: non-conflicting props such as className are forwarded.
• Children: rendered in the safe branch; not rendered in the unsafe branch.

Testing

npm run test -- src/components/tests/SafeLink.test.tsx src/utils/tests/url.test.ts

• SafeLink.test.tsx — 14 passing
• url.test.ts — 10 passing
• Consumers (ValidationDetail, ConfirmationModal, EvidenceUpload) — 49 passing, no regressions in link safety.