Add fresh CMake/platform scaffolding, core engine, and SDL3 window

Platform folders, cmake target/option/platform detection, Linux and PSP
scripts and Docker setup, assert/util/thread/error/log/perf/time/console/
engine/display modules, and an SDL3 window cleared to red.

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

scripts/psp/build.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+set -e
+cd "$(dirname "$0")/../.."
+if [ -z "$PSPDEV" ]; then
+  echo "PSPDEV environment variable is not set." >&2
+  exit 1
+fi
+psp-cmake -S . -B build-psp \
+  -DDUSK_TARGET_SYSTEM=psp \
+  -DBUILD_PRX=1 \
+  -DCMAKE_BUILD_TYPE=Release
+cmake --build build-psp -- -j"$(nproc)"