visitAllLinks: add a shouldVisit filter

[NullVoxPopuli]

Not every reachable link is one the crawl should assert on.

The case that prompted this: docs sites give demo components real-looking links whose route calls transition.abort(), so clicking one keeps the reader on the page instead of yanking them to a stub. Those targets aren't meaningfully visitable — in AuditBoard's docs app, visiting them makes visit() reject with TransitionAborted, so 7 otherwise-green pages failed the crawl with no app bug behind them. There was no way to tell the crawler "these are deliberately inert".

await visitAllLinks(undefined, undefined, {
  shouldVisit: (url) => !url.startsWith('/demo-targets/'),
});

Returning false skips the target entirely: not navigated to, not asserted on, and not traversed for further links. Beyond inert demo links it also covers sharding a large crawl across CI jobs (shouldVisit: (url) => hash(url) % SHARDS === INDEX) and excluding areas that have dedicated tests.

Tests: the test-app gains an /inert-demo-target route that aborts its transition, linked from the application template; every crawl in the suite now filters it out (realistic usage), and a new test asserts the filtered target is never visited while everything else still is, plus that a reject-everything filter visits nothing. Disabling the filter makes that test fail. 10/10 passing, lint clean.

One note on the fixture: a top-level aborting route in this test-app resolves rather than rejecting, so it demonstrates the filtering contract rather than reproducing the TransitionAborted rejection specifically — that came from a nested aborting route in a real app.

🤖 Generated with Claude Code