GUI provider deep-link test can dispatch hashchange twice #6009

Summary

gui/tests/providers-deep-link.test.tsx is flaky because its hash() helper both assigns location.hash and manually dispatches hashchange for every navigation. Happy DOM can also emit the native event for a changed hash, so the Accounts callback sometimes runs twice for one navigation.

Evidence

• GitHub Actions on fix(codex): surface remote provider-history filtering #6007 failed at line 112 with opened = ["alpha", "alpha", "alpha"] instead of two entries.
• A resource-capped isolated local run reproduced the same extra callback.
• The same test passed on an immediate control run and a repeated branch run, confirming timing-sensitive duplicate delivery rather than a deterministic fix(codex): surface remote provider-history filtering #6007 behavior change.

Expected fix

Make the helper mirror browser/navigation behavior:

• changed hash: assign the hash and rely on its normal event;
• unchanged hash: dispatch one explicit event, matching openProviderAccounts re-application semantics.

Keep the existing assertions for Back/Forward and repeating an unchanged Accounts link. Run the focused file repeatedly under an isolated DOM.