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]>

docker/linux/Dockerfile

@@ -0,0 +1,5 @@
+FROM ubuntu:latest
+ENV DEBIAN_FRONTEND=noninteractive
+WORKDIR /workdir
+COPY scripts/linux/install.sh /tmp/install.sh
+RUN chmod +x /tmp/install.sh && /tmp/install.sh && rm /tmp/install.sh