Tell user when they have reached the end of scrollback in FilePanel

### Your use case

#### What would you like to do?
Know when there are no more files to load (see #18489 and #18491)

#### Why would you like to it?
Because loading is sometimes dodgy and unreliable so I can't always tell if I've reached the oldest file

#### How would you like to achieve it?
- [ ] When the oldest file is reached, have an indicator (e.g. a string) above it which tells me that I am at the oldest file and there is nothing left to load
- [ ] The indicator does not show when the files between it and the newer files are still loading, it only shows when all loading is complete

### Have you considered any alternatives?

_No response_

### Additional context

_No response_