Fry3DX 0.5: builds for Windows, Linux and Android, a phone layout, Apache 2.0

- Apache License 2.0
- Windows: cross-built with clang-cl (cmake --preset windows), a window
  program with its icon; Linux: a portable preset (SDL and the C++
  library inside); Android: android/build_apk.py makes the APK
- tools/package.py packs the downloads; a GitHub workflow builds all
  three and makes a release for a v* tag
- A phone layout (fry_touch, on by default on Android): the UI drawn
  bigger, panels when asked for, a bar of big buttons, one finger to
  turn the view, two to move and pinch, a long press for a right-click;
  files through the phone's file picker
- Settings and autosaves now in a Nexoniarz folder (copied over once)
- README rewritten, the website shows the downloads and the phone

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NMSrd5oe1GpUD7E6d825KP

shell.nix

@@ -1,4 +1,6 @@
 # Dev shell for NixOS: `nix-shell`, then `cmake --preset debug && cmake --build build/debug`.
+# Windows builds too (cmake --preset windows, see cmake/toolchains/windows-msvc.cmake);
+# Android: android/shell.nix.
 { pkgs ? import <nixpkgs> {} }:
 pkgs.mkShell {
   packages = with pkgs; [
@@ -7,7 +9,10 @@ pkgs.mkShell {
     shaderc                       # glslc
     sdl3
     vulkan-loader vulkan-validation-layers vulkan-tools
+    llvmPackages_19.clang-unwrapped llvmPackages_19.lld llvmPackages_19.llvm xwin
   ];
   LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath (with pkgs; [ vulkan-loader sdl3 ]);
   VK_LAYER_PATH = "${pkgs.vulkan-validation-layers}/share/vulkan/explicit_layer.d";
+  # clang's own headers for the Windows cross compiler (Nix keeps them outside its resource dir).
+  KEEL_CLANG_INCLUDE = "${pkgs.llvmPackages_19.libclang.lib}/lib/clang/19/include";
 }