v0.2.0: clang + import std; isolated Windows cross-build (llvm-mingw + SDL3)

docs/ARCHITECTURE.md

@@ -1,7 +1,9 @@
 # Architecture
 
-OpenRA3 is organised as a stack of C++ modules. Each layer may import the ones
-below it, never the ones above.
+OpenRA3 is organised as a stack of C++26 modules. Each layer may import the ones
+below it, never the ones above. Every module uses `import std;` for the standard
+library; the engine is built with Clang + libc++ on Linux and cross-compiled
+with llvm-mingw for Windows.
 
 ```
                  ┌───────────────────────────────────────┐

docs/ROADMAP.md

@@ -14,6 +14,10 @@ that each one produces something that builds and runs.
 - [x] **v0.1.0 — map renderer + window.** Software ARGB framebuffer, TGA
       decoder for the map art, BMP output, map/grid/unit compositing, and an
       SDL3 window viewer (pan/zoom).
+- [x] **v0.2.0 — dual toolchain.** Switched to Clang + libc++ with
+      `import std;` in every module; added an isolated Windows cross-build
+      (llvm-mingw + SDL3 MinGW) producing `openra3.exe` + `SDL3.dll`, alongside
+      the Linux build. Both images are separate to keep the toolchains apart.
 
 ## Next