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]>

cmake/psp/target.cmake

@@ -0,0 +1,27 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+# Platform setup for the psp target, included by the root CMakeLists.txt.
+# Only sets defaults and definitions; the root applies them.
+
+# Source directories to build for this platform.
+set(DUSK_PLATFORM_DIRS duskpsp)
+
+# Default values for the shared options declared in the root CMakeLists.txt.
+# Assertions are faked (compiled out) unless this is a Debug build.
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+  set(DUSK_DEFAULT_ASSERTIONS_FAKED OFF)
+else()
+  set(DUSK_DEFAULT_ASSERTIONS_FAKED ON)
+endif()
+set(DUSK_DEFAULT_BACKTRACE OFF)
+set(DUSK_DEFAULT_TRACK_MEMORY OFF)
+
+# Platform definitions.
+set(DUSK_PLATFORM_DEFINITIONS
+  DUSK_PLATFORM_ENDIAN_LITTLE
+  DUSK_PSP
+  DUSK_THREAD_PTHREAD
+)