chore: Update spanish.yaml (#1717)

## Summary

Make this more transparent in Spanish:

`STR_AUTO_TURN_PAGES_PER_MIN: "Auto Turn (Pages Per Minute)"`

A weakness of the current translation is that the verb used is "to
read", but it's not clear that it is the user who will be reading a
certain amount of pages per minute. I've replaced it with the verb for
"to turn (pages)" which is the (analogous) physical action happening
regardless of who executes it, and the abbreviated adverb to clarify
that this is an automatic process. Lastly, a clarification of what the
number means in a simple proportion: "X pages in a minute". The Spanish
is very good overall, this one string is very hard to do in such a short
space. Even more so given that the number cannot be accompanied by any
units, so it must be clear from the text alone what it means.

## Additional Context

N/A

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

lib/I18n/translations/spanish.yaml

@@ -288,5 +288,5 @@ STR_FOOTNOTES: "Pie de página"
 STR_NO_FOOTNOTES: "No hay notas al pie de esta página"
 STR_LINK: "[enlace]"
 STR_SCREENSHOT_BUTTON: "Tomar captura de pantalla"
-STR_AUTO_TURN_ENABLED: "Páginas por minuto: "
-STR_AUTO_TURN_PAGES_PER_MIN: "Leer páginas por minuto"
+STR_AUTO_TURN_ENABLED: "Avance activado: "
+STR_AUTO_TURN_PAGES_PER_MIN: "Avance auto. (pág./min)"