Remove rpg, ui, editor and scene subfolders; split scripts by platform

Delete src/dusk/rpg, src/dusk/ui, the animation/keyframe modules, the
scene subfolders, the chunk asset loader and ./editor, and strip the
dependent save slot, scene type, engine and test code so the main
binary and tests build again. Add scene/node.c/.h skeleton and move
build scripts into scripts/<platform>/.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

scripts/vita/build-vita-docker.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+docker build -t dusk-vita -f docker/vita/Dockerfile .
+docker run --rm -v "$(pwd):/workdir" dusk-vita /bin/bash -c "./scripts/vita/build-vita.sh"

scripts/vita/build-vita.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+if [ -z "$VITASDK" ]; then
+  echo "VITASDK environment variable is not set. Please set it to the path of your VitaSDK installation."
+  exit 1
+fi
+
+mkdir -p build-vita
+cd build-vita
+cmake \
+  -DCMAKE_TOOLCHAIN_FILE=$VITASDK/share/vita.toolchain.cmake \
+  -DDUSK_TARGET_SYSTEM=vita \
+  ..
+make -j$(nproc)