docs: point Iceberg write comments to the consolidated user guide

spark/src/main/scala/org/apache/comet/serde/operator/IcebergWriteProtoTranslation.scala

@@ -199,7 +199,8 @@ object IcebergWriteProtoTranslation {
    * zstd (parquet-rs default 1, parquet-mr default 3). To produce files the same size as
    * iceberg-java would, substitute parquet-mr's 3 when zstd is in use and the user did not set an
    * explicit level. gzip defaults to 6 on both sides; snappy and lz4 have no level concept;
-   * compressed bytes are an accepted divergence regardless (see iceberg-writes.md).
+   * compressed bytes are an accepted divergence regardless (see "Accepted divergences" under
+   * Writes in `docs/source/user-guide/latest/iceberg.md`).
    */
   private def resolveCompressionLevel(
       props: Map[String, String],

spark/src/test/scala/org/apache/comet/CometIcebergWriteActionSuite.scala

@@ -4901,7 +4901,8 @@ class CometIcebergWriteActionSuite
   // What is asserted here is determinism, not parity: iceberg-java's fanout writer iterates its
   // own `StructLikeMap`, so the two writers only agree where that map order and path order happen
   // to coincide -- which they do for the ascending partition values the upstream test uses. See
-  // the fanout entry under accepted divergences in `iceberg-writes.md`.
+  // the fanout ordering entry in "Accepted divergences" under Writes in
+  // `docs/source/user-guide/latest/iceberg.md`.
   //
   // Eight partitions rather than the two that test uses: an unfixed writer lands in path order by
   // luck 1 time in 8!, where with two it would pass half the time.

spark/src/test/scala/org/apache/spark/sql/benchmark/CometIcebergEndToEndBenchmark.scala

@@ -60,8 +60,8 @@ import org.apache.comet.CometSparkSessionExtensions
  *   - The timed statement includes the driver-side Iceberg commit, which all three configurations
  *     pay equally.
  *   - The warehouse is a local temporary directory, so no object-store latency is included.
- *   - The two writers choose different file roll points (see the accepted divergences in
- *     `docs/source/user-guide/latest/iceberg-writes.md`), so the resulting file layouts are not
+ *   - The two writers choose different file roll points (see "Accepted divergences" under Writes
+ *     in `docs/source/user-guide/latest/iceberg.md`), so the resulting file layouts are not
  *     expected to match. What is checked is that every configuration writes the same rows.
  *   - Every group has the same row count but not the same row width, so `Rate` and `Per Row`
  *     compare configurations within a group, not one group with another.

spark/src/test/scala/org/apache/spark/sql/benchmark/CometIcebergWriteBenchmark.scala

@@ -60,8 +60,8 @@ import org.apache.comet.CometSparkSessionExtensions
  *   - The timed statement includes the driver-side Iceberg commit, which all three configurations
  *     pay equally. It dilutes the writer's factor rather than inflating it.
  *   - The warehouse is a local temporary directory, so no object-store latency is included.
- *   - The two writers choose different file roll points (see the accepted divergences in
- *     `docs/source/user-guide/latest/iceberg-writes.md`), so the resulting file layouts are not
+ *   - The two writers choose different file roll points (see "Accepted divergences" under Writes
+ *     in `docs/source/user-guide/latest/iceberg.md`), so the resulting file layouts are not
  *     expected to match. Only wall clock and row counts are compared.
  *   - `Rate` and `Per Row` are always computed against the corpus size, so for the `DELETE` case
  *     they describe the rows the statement passed over, not the far smaller number it removed.