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

engine/rhi/vulkan/vk_backend.cpp

@@ -1,5 +1,6 @@
 // The Vulkan 1.3 backend: bindless textures (one descriptor array), buffer device addresses
 // for every per-draw and per-frame buffer (passed in push constants), dynamic rendering.
+#include "ui/ui.h"
 #include "render/backend.h"
 #include "render/screenshot.h"
 #include "rhi/vulkan/vk_device.h"
@@ -398,6 +399,7 @@ public:
     void beginUi() override {
         ImGui_ImplVulkan_NewFrame();
         ImGui_ImplSDL3_NewFrame();
+        ui::applyPixelScale();
         ImGui::NewFrame();
     }
     void setVsync(bool on) override { device_.setVsync(on); }