Fix sun quad visibility, minimap opacity, audio scaling, and rename music toggle

- Tighten celestial glow falloff and edge fade to eliminate visible quad boundary
- Add opacity support to minimap display shader, synced with UI opacity setting
- Fix audio double/triple-scaling by removing redundant master volume multiplications
- Rename "Original Soundtrack" toggle to "Enable WoWee Music"
- Add About tab with developer info and GitHub link

src/rendering/minimap.cpp

@@ -30,7 +30,8 @@ struct MinimapDisplayPush {
     float arrowRotation;
     float zoomRadius;
     int32_t squareShape;
-};  // 40 bytes
+    float opacity;
+};  // 44 bytes
 
 Minimap::Minimap() = default;
 
@@ -529,6 +530,7 @@ void Minimap::render(VkCommandBuffer cmd, const Camera& playerCamera,
     push.arrowRotation = arrowRotation;
     push.zoomRadius = zoomRadius;
     push.squareShape = squareShape ? 1 : 0;
+    push.opacity = opacity_;
 
     vkCmdPushConstants(cmd, displayPipelineLayout,
                        VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT,