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

content/engine/cfg/default.cfg

@@ -0,0 +1,3 @@
+// Fry3DX: no game keys (the app reads its own). Your settings are saved after this.
+unbindall
+bind f8 devmenu

content/engine/skies/CREDITS.txt

@@ -0,0 +1,4 @@
+skies/day.hdr: "Kloofendal 48d Partly Cloudy (Pure Sky)" by Greg Zaal and Jarod Guest, Poly Haven, CC0 1.0 (public domain)
+https://polyhaven.com/a/kloofendal_48d_partly_cloudy_puresky
+skies/afternoon.hdr: "Qwantani Afternoon (Pure Sky)" by Greg Zaal and Jarod Guest, Poly Haven, CC0 1.0 (public domain)
+https://polyhaven.com/a/qwantani_afternoon_puresky