The "return the last array entry's error" branch in package_target_resolve was dead code: i comes from enumerate(), so i == targets.len() could never be true. Errors from array entries were always swallowed like undefined, so an invalid target in the last fallback entry surfaced as a generic PackagePathNotExported instead of the specific error — despite the comment right below claiming "Return or throw the last fallback resolution null return or error".

This fixes the off-by-one (i + 1 == targets.len()) so the last entry's error now propagates, matching the documented intent and Node's lastException behavior for arrays.

One deliberate exemption: ResolveError::NotFound still falls through. It only arises from re-resolving a bare imports target (e.g. \"#a\": [{\"import\": [\"#b/import.js\"]}]) through the module system, and enhanced-resolve treats an unresolvable candidate there as a soft failure, not a hard error — the ported "Direct and conditional mapping #4" test pins that behavior. Node would actually throw immediately on any non-ERR_INVALID_PACKAGE_TARGET error inside the array loop, which is stricter than enhanced-resolve; the exemption keeps us compatible with the latter.

Adds two imports-field tests: an invalid target in the last array entry now errors (previously Ok(None)), and an invalid target in a non-last entry still falls through to the next entry.

Split out of #1263.