Add complete game working copy under assets/ (runtime data + binaries)

Imports the full shipped working copy of Red Planet v4.10 so the repo is
self-contained: buildable (source) and runnable (data). ~110 MB, committed
directly to git per project decision.

Contents (assets/RP411/):
- AUDIO/  (~97 MB) 223 .wav + audio config/res
- VIDEO/  (~10 MB) .X meshes, .SKL/.det/.sph geometry, .met materials,
          .pcc/.png/.pcx textures, .vsh/.psh shaders, material tables
- GAUGE/  (~0.8 MB) HUD .GIM images, .PCC/.PCX bitmaps, gauge config
- SPOOLS/ runtime replay output dir (kept via .gitkeep)
- Root config/launch: environ.ini, RPDPL.INI, JOYSTICK.INI, TEST.EGG,
  RPL4.RES, *.bat launchers
- Runtime binaries: rpl4opt.exe (shipped reference build), libsndfile-1.dll,
  oalinst.exe (OpenAL redist installer), sleep.exe

Housekeeping:
- .gitignore: re-include assets/**/*.exe and *.dll (global rules skip them);
  keep Thumbs.db and runtime *.spl out.
- .gitattributes: mark asset media (.wav/.png/.pcc/.gim/.x/.skl/... ) binary.
- docs/ASSETS.md: runtime layout, config chain (environ.ini -> RPDPL.INI ->
  video/audio/gauge paths), launch args, and per-directory asset inventory.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitattributes

@@ -28,3 +28,27 @@
 *.egg  binary
 *.EGG  binary
 *.rtf  binary
+
+# Game runtime assets (under assets/) — always binary, never EOL-normalized
+*.wav  binary
+*.png  binary
+*.pcx  binary
+*.PCX  binary
+*.pcc  binary
+*.PCC  binary
+*.gim  binary
+*.GIM  binary
+*.x    binary
+*.X    binary
+*.skl  binary
+*.SKL  binary
+*.det  binary
+*.sph  binary
+*.met  binary
+*.gat  binary
+*.GAT  binary
+*.sky  binary
+*.vsh  binary
+*.psh  binary
+*.dll  binary
+*.exe  binary