docs: add Stackmon game setup notes and games directory

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gaming/CONTEXT.md

@@ -44,6 +44,8 @@ For per-game settings (RT, DLSS, HDR, retro games), see the **steam-game-setup**
 /gaming/
 ├── CONTEXT.md              # This file - technology overview
 ├── troubleshooting.md      # Error handling and debugging
+├── games/                  # Per-game setup notes
+│   └── stackmon.md        # Stackmon (3729550)
 ├── examples/               # Working configurations and templates
 │   ├── ready-or-not/      # Ready or Not specific configs
 │   └── nvidia-optimized/  # NVIDIA-specific game configs

gaming/games/stackmon.md

@@ -0,0 +1,33 @@
+# Stackmon
+
+| Field | Value |
+|-------|-------|
+| **Steam App ID** | 3729550 |
+| **Developer** | Riftpoint Entertainment |
+| **Engine** | Unknown (likely Unity) |
+| **Graphics API** | DX10/DX11 |
+| **Status** | Playtest (Q2 2026 release) |
+| **Genre** | Creature-collector / card-stacking |
+| **STL Profile** | `~/.config/steamtinkerlaunch/gamecfgs/id/3729550.conf` |
+| **Setup Date** | 2026-03-02 |
+
+## Features
+
+| Feature | Supported |
+|---------|-----------|
+| Ray Tracing | No |
+| DLSS | No |
+| HDR | No |
+
+## Configuration Notes
+
+- Standard DX11 config - no special features enabled
+- Very lightweight requirements (3GHz CPU, 4GB RAM, 3GB GPU)
+- No customvars file needed
+- No ProtonDB reports available yet (playtest phase)
+
+## Proton Compatibility
+
+- Using Proton 9.0-4 (default)
+- If issues arise during playtest, try GE-Proton or Proton Experimental
+- MangoHud should show `API: VK` (DXVK translating DX11)