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-docker.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+set -e
+cd "$(dirname "$0")/../.."
+docker build -t dusk-linux -f docker/linux/Dockerfile .
+docker run --rm -v "$(pwd):/workdir" dusk-linux /bin/bash -c "./scripts/linux/test.sh"