remove sdl subtree and update

flake.nix

@@ -10,9 +10,13 @@
       url = "github:nlohmann/json/v3.11.3"; # TODO: read version from file
       flake = false;
     };
+    sdl3 = {
+      url = "github:libsdl-org/SDL/0429f5d6a36fc35b551bcc2acd4a40c2db6dab82"; # keep in sync this cmake
+      flake = false;
+    };
   };
 
-  outputs = { self, nixpkgs, flake-utils, nlohmann-json }:
+  outputs = { self, nixpkgs, flake-utils, nlohmann-json, sdl3 }:
     flake-utils.lib.eachDefaultSystem (system:
     let
       pkgs = import nixpkgs { inherit system; };
@@ -69,6 +73,7 @@
           # TODO: use package instead
           "-DFETCHCONTENT_SOURCE_DIR_ZSTD=${pkgs.zstd.src}" # we dont care about the version (we use 1.4.x features)
           "-DFETCHCONTENT_SOURCE_DIR_LIBWEBP=${pkgs.libwebp.src}"
+          "-DFETCHCONTENT_SOURCE_DIR_SDL3=${sdl3}"
         ];
 
         # TODO: replace with install command