Docs: Delta Lake migration Output table names a result that does not exist

**Apache Iceberg version**

main @ 5f3d3c560

**Query engine**

None — the affected action is the engine-agnostic `delta-lake` Java API.

**Please describe the bug**

The Output table in `docs/docs/delta-lake-migration.md` (line 87) documents the result of the `snapshotDeltaLakeTable` action as `imported_files_count`. No such name exists in the `delta-lake` module.

`SnapshotDeltaLakeTable.Result` (`delta-lake/src/main/java/org/apache/iceberg/delta/SnapshotDeltaLakeTable.java` lines 85-91) declares exactly one method: `long snapshotDataFilesCount()`.

`imported_files_count` is the output column of the Spark `snapshot` SQL procedure, defined in `SnapshotTableProcedure`. The delta row is character-identical to `docs/docs/spark-procedures.md` line 618, so it was copied from the Spark page. It has never matched the delta-lake API — the module's original commit already declared `snapshotDataFilesCount()` only.

**Steps to reproduce**

1. Read the Output table on the Delta Lake migration page.
2. Run the Examples snippet on the same page and call the documented name on the returned `Result`.

Expected: the documented name resolves. Actual: only `snapshotDataFilesCount()` exists, so no such member can be found.

**Additional context**

The page documents the Java API only — it contains no SQL procedure call, and the Usage table lists Java configuration methods. Fix is one line: rename the output to `snapshotDataFilesCount`. The `Type` column (`long`) already matches the declaration.

Open docs/docs/delta-lake-migration.md around line 87 and compare its Output table with delta-lake/src/main/java/org/apache/iceberg/delta/SnapshotDeltaLakeTable.java around lines 85-91. Confirm the page documents the engine-agnostic Java API, then check the documentation validation workflow. Done means the documented result name matches SnapshotDeltaLakeTable.Result.snapshotDataFilesCount() and the existing type remains long.

Written by the indexing model from the issue text.