Image letterboxing inconsistent between chapters

### Differences in behavior between chapters

The behavior for letterboxing is different across chapters:

- "Mod" branch + Ch[1, 2]: Left and right black bars only
- In other words, the image height is clamped to the window height, then the width is set to keep the same aspect ratio. Tall images are OK, but images wider than the window will be cut-off
- Console + Ch[3, 4, 5, **7**]: Both Left and right black bars, and top and bottom black bars are supported
- Ch[6, **8**, 9, 10 (hou)] : In addition to both types of letterboxing, ONLY when origin is non-null, special cases are added for specific width and heights:
- A height of 960 is converted to a height of 480
- A width of 1280 is converted to a width of 640
- I don't actually know if this does anything extra compared to normal?

Oddly, chapter 7 is an outlier and doesn't follow the "add new features every N chapters" pattern.

Also, I'm pretty sure we never use non-null origin (originx set to 0), refer to:
- https://github.com/07th-mod/higurashi-assembly/issues/142

### Conclusion

All this taken into account, it more or less means that Chapter 1 and 2 behave differently to all the other chapters with respect to image scaling. This can be easily fixed, but for chapter 1 and 2 this may cause some graphical bugs, if we are accidentally relying on the old behavior.

Das Issue beschreibt inkonsistentes Letterboxing-Verhalten von Bildern über verschiedene Kapitel des Spiels hinweg. Beginnen Sie mit der Untersuchung des Bild-Rendering-Codes, wahrscheinlich in Dateien, die Grafik- oder UI-Skalierung behandeln. Suchen Sie nach bedingter Logik basierend auf Kapitelnummern. Überprüfen Sie das verlinkte Issue #142 für Kontext zur Verwendung von non-null origin. Das Testen von Änderungen erfordert das Ausführen verschiedener Kapitel, um zu überprüfen, dass der Fix keine grafischen Regressionen einführt.

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