Unhandled promise rejections when navigations are superseded/aborted

[uhyo]

Found during a library audit (see AUDIT.md on branch claude/library-audit-sxpugz, §1.9). Code-level finding against v1.1.1 — not verified empirically (the test mock's navigate() always resolves), so first step is a repro/regression test with a rejecting finished promise.

Problem

navigation.navigate().finished rejects (typically AbortError) when a navigation is interrupted by a newer one, or prevented. Several fire-and-forget paths discard that rejection:

• NavigationAPIAdapter.navigate() ignores the returned { committed, finished } entirely (packages/router/src/core/NavigationAPIAdapter.ts).
• setSearchParams does void navigateAsync(...) (packages/router/src/hooks/useSearchParams.ts) — rapid successive calls (e.g. typing in a search box that syncs to the URL) abort each other.
• User code calling the async setState without await/.catch hits the same via navigateAsync.

Expected result: console noise from unhandledrejection events, and potentially error-tracking alerts in production apps.

Suggested fix

Attach a no-op .catch on internal fire-and-forget paths (abort of a superseded navigation is expected behavior, not an error), while still propagating rejection to callers who explicitly await navigateAsync. The mock in src/__tests__/setup.ts could gain a way to make finished reject so this path is testable.