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/psp/build-psp-docker.sh

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

scripts/psp/build-psp.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+if [ -z "$PSPDEV" ]; then
+  echo "PSPDEV environment variable is not set. Please set it to the path of your PSP development environment."
+  exit 1
+fi
+
+mkdir -p build-psp
+cd build-psp
+psp-cmake -DDUSK_TARGET_SYSTEM=psp -DCMAKE_TOOLCHAIN_FILE=$PSPDEV/psp/share/pspdev.cmake -DBUILD_PRX=1 .. CMAKE_BUILD_TYPE=Release
+make -j$(nproc)
+# psp-cmake -DDUSK_TARGET_SYSTEM=psp -DCMAKE_TOOLCHAIN_FILE=$PSPDEV/psp/share/pspdev.cmake -DBUILD_PRX=1 -DCMAKE_BUILD_TYPE=Debug ..
+# make