OG sprites lower quality than previous chapters / Use Hou+ Sprites

Currently for Rei we use the low resolution (`640x480`) sprites that come with the unmodded game.

Previous chapters use upscaled versions of these sprites, upscaled to `1280x960` resolution. I don't remember what upscaling we used though, I will have to check git or discord history.

However, there was some discussion whether we could use the high resolution Hou+ sprites for our OG sprites, since those are naturally high resolution (or at least look sharper than upscaled sprites). I'm not sure whether the Hou+ sprites would cover all the sprites we have in the mod, though - I haven't even looked at them myself yet.

So there are two things to be done for this issue, one to make this chapter consistent with previous chapters, and one to overhaul all the OG sprites:
- [ ] Upscale the existing sprites to fix this issue quickly (or just proceed with below first)
- [ ] In the long term, use the mapping in https://github.com/drojf/match_higurashi_scripts and the Hou+ sprites to regenerate all the OG sprite packs.

Also see https://github.com/07th-mod/higurashi-rei/issues/10 "OG Sprites / Backgrounds Known Issues"

Zuerst die vorhandenen Sprite-Dateien im Projekt prüfen, um die aktuelle Auflösung und Benennung zu verstehen. Dann die Zuordnung unter https://github.com/drojf/match_higurashi_scripts überprüfen und mit dem Hou+-Sprite-Pack vergleichen, um die Abdeckung zu sehen. 'Erledigt' bedeutet, dass alle OG-Sprites entweder auf 1280x960 hochskaliert oder durch höherwertige Hou+-Sprites ersetzt wurden, wobei die Konsistenz mit vorherigen Kapiteln sichergestellt wird.

Vom Indexierungsmodell aus dem Issue-Text verfasst.