Adds List<String> instanceIds to LogSearchRequest (null-normalized to
List.of() in compact ctor) and generates an IN clause in both
ClickHouseLogStore.search() and countLogs(), mirroring the existing
sources pattern. LogQueryController parses ?instanceIds= as a
comma-split list. All existing LogSearchRequest call sites updated.
New ClickHouseLogStoreInstanceIdsIT covers: multi-value filter, empty
filter (all rows), null filter (all rows), single-value filter, and
coexistence with the singular instanceId field.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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