test: dedupe isDefined helper against the library util

[mbret]

Summary

src/tests/liveQuery.tsx defined its own isDefined type-guard:

export function isDefined<T>(value: T | undefined | null): value is T {
  return value != null
}

This is a runtime-identical copy of the shipped src/lib/utils/isDefined.ts. The two live-query test suites now import isDefined from the library util directly, and the local copy is deleted — one implementation instead of two.

Behavior-preserving: the query pipes and assertions are unchanged; only the source of isDefined moved.

Net LOC

2 insertions, 6 deletions → net −4 lines across 3 files.

Note

An earlier revision of this PR also extracted the repeated live-query queryFn pipe into a createLiveQueryFn factory in the shared test helper. That was reverted — a test-only closure factory living in the source tree wasn't a good trade, so the inline pipes are left as-is.

Gates

All green locally: biome check, tsc, vite build, vitest run (129 tests).

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