Enhance audio management and documentation

Added a MasterVolume property to the AudioManager for unified control over sound effects and music volume. Updated the Play method to incorporate MasterVolume adjustments. Enhanced documentation in CLAUDE.md and architecture.md to reflect changes in audio management and overall engine architecture. Introduced a new test project for audio functionalities in the solution file.

CLAUDE.md

@@ -27,13 +27,15 @@ is the living showcase — new engine features are demonstrated there.
 
 Engine libraries (each feature is a namespaced subfolder of its host):
 
-- **`Core`** — game loop, ECS world, scenes, time, plus **Input** (`MrGameEng.Input`:
-  `InputManager`, `ActionMap`, `InputSystem`, in `Core/Input/`). Depends only on
-  MonoGame and Friflo.Engine.ECS.
+- **`Core`** — game loop, ECS world, scenes, time (`GameClock` with `TimeScale`; `GameSpeed`
+  for discrete pause/1×/3×/6× speed control over the clock, `context.UseGameSpeed(...)`),
+  plus **Input** (`MrGameEng.Input`: `InputManager`, `ActionMap`, `InputSystem`, in
+  `Core/Input/`). Depends only on MonoGame and Friflo.Engine.ECS.
 - **`Graphics`** — custom batched renderer, camera, sprites, plus **Tilemaps**
   (`MrGameEng.Tilemaps`: code-built tile grids rendered through the batcher,
   `scene.UseTilemaps()` after `UseRenderer2D()`, in `Graphics/Tilemaps/`). → `Core`.
-- **`Audio`** — ogg playback (NVorbis). → `Core`.
+- **`Audio`** — ogg playback (NVorbis); `AudioManager` with `SoundVolume`/`MasterVolume`
+  (one knob for effects + music). → `Core`.
 - **`Content`** — the asset/content pipeline: **Assets** (`MrGameEng.Assets`: runtime
   loading, no MGCB pipeline; FontStash), **Atlases** (`MrGameEng.Atlases`: texture-atlas
   builder + runtime loader, CLI wrapper in `tools/MrGameEng.AtlasTool`; StbImage), and