[PDF] Feature request for Baader: Parse ex-date during dividend import

### Affected Bank

Baader

### Pdf2Txt

```
PDFBox Version: 3.0.6
Portfolio Performance Version: 0.82.0
System: linux
-----------------------------------------
[...]
Referenz-Nr.: 123
Fondsausschüttung
Ex-Tag: 01.01.2026
Nominale ISIN: FOO WKN: BAR Ausschüttung
[...]
```

### Issue Description

Parse ex-date during dividend import 