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/linux/test.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -e
+cd "$(dirname "$0")/../.."
+rm -rf build-tests
+cmake -S . -B build-tests -DDUSK_BUILD_TESTS=ON -DDUSK_TARGET_SYSTEM=linux
+cmake --build build-tests -- -j"$(nproc)"
+ctest --output-on-failure --test-dir build-tests