Split the simulation from presentation into an SDL-free library

Sim holds one whole game (tick, snapshots, checksum) and talks to the screen only
through Cues, which the client's Scene plays and the server ignores. All drawing
moved to scene.cpp. Match takes this screen's wishes as request flags instead of
reading the menu, input and settings. The sim library builds without SDL and the
server links it, ready to run games itself.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/effects.h

@@ -5,20 +5,6 @@
 
 struct Game;
 
-// Describes a spray of square particles, fanned around angle by spread. Fill is how far their colour takes over their
-// black middle.
-struct Burst
-{
-    float angle = 0;
-    float fill = 0;
-    float gravity = 0;
-    float life = 0.4f;
-    float size = 3;
-    float speed = 100;
-    float spread = PI;
-    int count = 8;
-};
-
 struct Particle
 {
     Color color;
@@ -70,13 +56,10 @@ struct Afterimage
     float life = 0;
 };
 
-// Particles, afterimages, text popups, screen shake and the damage-per-second tally. While muted (during a
-// rollback replay) it ignores new requests.
+// Particles, afterimages, text popups, screen shake and the damage-per-second tally.
 class Effects
 {
 public:
-    bool isMuted = false;
-
     void burst(Burst burst, Vec2 position, float angle, Color color);
     void afterimage_spawn(Pose pose);
     void flash_spawn(Vec2 position, float angle, float size, Color color);