Investigate XLS parsing failure in packaged Gradle JAR and define required Excel dependencies

From @zaleslaw

### Problem

A user reported failure when reading `.xls` files from a packaged Gradle JAR:

Your InputStream was neither an OLE2 stream, nor an OOXML stream
or you haven't provide the poi-ooxml*.jar in the classpath/modulepath

However, there is no minimal reproducible example, so it is unclear whether:
- this is a DataFrame issue,
- a packaging issue,
- or a project configuration problem.

### Expected

Clarify expected behavior and requirements for Excel parsing in packaged applications.

### Acceptance criteria

- Verify whether `.xls` reading works in a packaged Gradle JAR with correct dependencies
- If reproducible:
- identify root cause and fix if needed
- If not reproducible:
- document required POI dependencies and setup for packaged apps
- Ensure error message is understandable for missing dependencies

### Motivation

- Excel IO is a user-facing feature
- Packaged applications are a common usage scenario
- Even unconfirmed reports indicate potential confusion around setup
- Clear behavior and documentation reduce ambiguity before 1.0

From @langbiantianya

```
2023-07-12 14:52:06 14:52:06.262 [DefaultDispatcher-worker-6] ERROR c.c.g.app.router.rest.UploadRouter - Your InputStream was neither an OLE2 stream, nor an OOXML stream or you haven't provide the poi-ooxml*.jar in the classpath/modulepath - FileMagic: OLE2, having providers: [org.apache.poi.xssf.usermodel.XSSFWorkbookFactory@234c7887]
2023-07-12 14:52:06 java.io.IOException: Your InputStream was neither an OLE2 stream, nor an OOXML stream or you haven't provide the poi-ooxml*.jar in the classpath/modulepath - FileMagic: OLE2, having providers: [org.apache.poi.xssf.usermodel.XSSFWorkbookFactory@234c7887]
```