raincloud: flip oasst1 to ok — #270 fixed

The CsvExporter null-struct-row fix (render a fully-null nested Struct row as
an empty CSV cell instead of {"field":null,...}), merged in #275 (commit
70b7848), closes the oasst1 conformance gap tracked by #270.

Confirmed by re-running RaincloudConformanceIntegrationTest#conformancePerSlug
scoped to the hydrated corpus (forkCount=0): before the flip, oasst1's
gap-arm assertion fired "known gap gap:270 no longer reproduces" (the export
now succeeds and matches the parquet oracle exactly); after flipping the entry
to ok the whole 130-slug factory is green (Tests run: 130, Failures: 0),
proving the ok-arm assertMatchesParquetOracle path passes for oasst1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: dfa1

integration/src/test/resources/raincloud/expected-status.csv

@@ -156,7 +156,7 @@ nyc-311,untriaged
 nyc-parking-tickets,untriaged
 nyc-property-sales,ok
 nypd-complaints,untriaged
-oasst1,gap:270
+oasst1,ok
 open-food-facts,untriaged
 openlibrary-authors,untriaged
 openlibrary-editions,untriaged