fix(security): link warning no longer bypassed by a sentence or shared hosting (#335)

Two easy bypasses of the "this link goes somewhere else" check:

- Any whitespace in the link text disabled it, so "Log in at
  chat.lotusguild.org" → evil.example wasn't flagged. hostsFromText now
  scans each word for host-shaped tokens; a link is flagged if any named
  host is a different site. Bare file names (main.py, report.pdf) and
  version numbers are skipped inside sentences so ordinary links aren't
  flagged.
- Shared-hosting suffixes counted as one site (alice.github.io vs
  evil.github.io, *.pages.dev, netlify.app, vercel.app, …).
  registrableDomain now treats a curated list of them as public suffixes
  (longest match, incl. s3.amazonaws.com). Curated rather than the full
  PSL to stay inside the bundle budget.

Verified with unit tests and headless on real messages: the four bypass
cases are flagged; the honest sentence, file/version text and "click
here" are not.

Fixes #335

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/utils/linkSafety.test.ts

@@ -38,3 +38,38 @@ test('hostFromText only accepts URL/host-shaped text; IDN becomes punycode', ()
   assert.equal(analyzeLink('paypal.com', 'https://xn--pypal-4ve.com/')?.punycode, true);
   assert.equal(analyzeLink('paypal.com', 'https://xn--pypal-4ve.com/')?.mismatch, true);
 });
+
+test('a trusted name inside a sentence still exposes a different destination (#335)', () => {
+  const a = analyzeLink('Log in at chat.lotusguild.org', 'https://evil.example/');
+  assert.equal(a?.mismatch, true);
+  assert.equal(a?.shownHost, 'chat.lotusguild.org');
+  assert.equal(
+    analyzeLink('chat.lotusguild.org (official)', 'https://evil.example/')?.mismatch,
+    true,
+  );
+  assert.equal(
+    analyzeLink('Open https://paypal.com/login now', 'https://evil.example/')?.mismatch,
+    true,
+  );
+  // honest sentences are not flagged
+  assert.equal(
+    analyzeLink('Log in at chat.lotusguild.org', 'https://chat.lotusguild.org/login')?.mismatch,
+    false,
+  );
+  assert.equal(analyzeLink('read the docs', 'https://evil.example/')?.mismatch, false);
+  assert.equal(analyzeLink('see main.py and report.pdf', 'https://github.com/x')?.mismatch, false);
+  assert.equal(analyzeLink('release v1.2.3 notes', 'https://github.com/x')?.mismatch, false);
+});
+
+test('shared hosting suffixes are separate sites (#335)', () => {
+  assert.equal(registrableDomain('alice.github.io'), 'alice.github.io');
+  assert.equal(registrableDomain('www.alice.github.io'), 'alice.github.io');
+  assert.equal(registrableDomain('bucket.s3.amazonaws.com'), 'bucket.s3.amazonaws.com');
+  assert.equal(analyzeLink('alice.github.io', 'https://evil.github.io/')?.mismatch, true);
+  assert.equal(analyzeLink('lotusguild.pages.dev', 'https://evil.pages.dev/')?.mismatch, true);
+  assert.equal(
+    analyzeLink('alice.github.io/blog', 'https://alice.github.io/blog/1')?.mismatch,
+    false,
+  );
+  assert.equal(registrableDomain('news.bbc.co.uk'), 'bbc.co.uk');
+});