Fix ListObjectsV2 pagination snapshot inconsistency

[Copilot]

ListObjectsV2 loaded bucket metadata at an initial readTS, then silently replaced readTS with token.ReadTS from the continuation token — leaving meta.Generation derived from a different snapshot than the actual scan. This could cause incorrect token validation or mis-keyed scans when bucket state changed between pages.

Changes

• adapter/s3.go — listObjectsV2: Reorder initialization so the continuation token is parsed first, the final readTS is resolved (token.ReadTS if present, otherwise s.readTS()), and bucket metadata is loaded at that resolved timestamp before any token validation occurs.

// Before: meta loaded at initial readTS, then readTS replaced without reloading meta
readTS := s.readTS()
meta, _, _ := s.loadBucketMetaAt(ctx, bucket, readTS)
token, _ := decodeS3ContinuationToken(...)
if token != nil && token.ReadTS != 0 {
    readTS = token.ReadTS  // meta now inconsistent with readTS
}

// After: token parsed first, single consistent readTS used for meta load
token, _ := decodeS3ContinuationToken(...)
readTS := s.readTS()
if token != nil && token.ReadTS != 0 {
    readTS = token.ReadTS
}
meta, _, _ := s.loadBucketMetaAt(ctx, bucket, readTS)  // consistent snapshot

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