Add engine-debug-tools and fix critter animation rendering bugs

- engine-debug-tools/: a debug dump hotkey + dump2png to inspect
  decoded critter frames independent of the renderer (see root
  README.md's "Debugging" section).
- engine-patches/04,05: fix critter sprite scale and an OpenGL
  texture cache collision, found using that tooling.
- mdlp: fix encodeFrames RLE-diffing upscaled frames against a
  previous-frame reference the real RSD8 decoder never implements
  (verified against Night Dive's original Mac source down to the
  68K assembly) - was rendering as scattered static in-game.
- Upscale pipeline: better color quantization (dithering, pure-ramp
  exclusion) and per-resource model selection.

engine-debug-tools/dump2png/go.mod

@@ -0,0 +1,12 @@
+module questshock/dump2png
+
+go 1.25.0
+
+// hacked/ is vendored under modding/src/ (see ../../modding/README.md);
+// dump2png reuses its resource/palette reading code (ss1/world,
+// ss1/content/bitmap) instead of duplicating System Shock's file formats.
+require github.com/inkyblackness/hacked v0.0.0
+
+require github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
+
+replace github.com/inkyblackness/hacked => ../../modding/src/hacked