* Group export feeds by category
## What changed
- Groups feed choices in the import/export page by their existing FreshRSS category.
- Preserves the current export request format and selection behavior.
## Why
The export selector previously mixed feeds from every category, making a category-specific export difficult to assemble.
Closes#5555
* Declare export feed count view data
* Fix select size
---------
Co-authored-by: Gerard Alvear <gerard.alvear@logiqd.me>
Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>
dd2ef8ffa6