docs(reader): correct zone-alignment claim and stale ZonedStatsSchema ref

columnZoneStats javadoc overstated alignment: zone-map rows align with
chunkRowCounts() only on the fallback path and for files this writer
produces (one zone per chunk). A foreign writer may use a fixed zone
length independent of chunk boundaries, so the zone count need not match.
Reword to scope the guarantee.

Also fix VortexWriter's stale [io.github.dfa1.vortex.inspect] reference to
ZonedStatsSchema — the class moved to the reader package in this branch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

reader/src/main/java/io/github/dfa1/vortex/reader/ScanIterator.java

@@ -402,10 +402,15 @@ public long[] chunkRowCounts() {
     /// without touching any data segment. This is the source Rust populates for `SUM`, so the
     /// values match files written by either implementation. When no zone map is present the
     /// list falls back to each chunk's embedded `ArrayStats` (min/max/null count; `sum` is
-    /// `null`, since the flat writer does not retain it). Either way the result has one entry
-    /// per chunk/zone, positionally aligned with [#chunkRowCounts()]; a column that is absent
+    /// `null`, since the flat writer does not retain it). Either way a column that is absent
     /// or carries no stats yields [ArrayStats#empty()] per zone.
     ///
+    /// Zone granularity is the layout's, not the scan's. The fallback path is one entry per
+    /// chunk, positionally aligned with [#chunkRowCounts()]. The zone-map path is one entry per
+    /// zone of the stats table: this writer emits one zone per chunk (so the same alignment
+    /// holds), but a file from another writer may use a fixed zone length independent of chunk
+    /// boundaries, in which case the zone count need not match [#chunkRowCounts()].
+    ///
     /// This is the read-side surface for aggregate push-down (ADR 0013 §6): a reduction can
     /// fold whole zones from these rows and fall back to a streaming decode only for the
     /// boundary zones a predicate partially selects.

writer/src/main/java/io/github/dfa1/vortex/writer/VortexWriter.java

@@ -821,7 +821,7 @@ private int wrapZoneMap(FbsBuilder fbb, String colName, int dataLayout, long col
 
     /// `vortex.stats` metadata: `u32` zone length (LE) + a 1-byte stat bitset (LSB-first) with the
     /// NULL_COUNT bit always set and the MAX/MIN and SUM bits set when present, matching
-    /// [io.github.dfa1.vortex.inspect] `ZonedStatsSchema`.
+    /// [io.github.dfa1.vortex.reader] `ZonedStatsSchema`.
     private static byte[] zonedMetadataBytes(long zoneLen, boolean hasMinMax, boolean hasSum) {
         byte[] meta = new byte[5];
         ByteBuffer.wrap(meta).order(ByteOrder.LITTLE_ENDIAN).putInt((int) zoneLen);