feat: init nix flake

src/app.ts

@@ -168,7 +168,7 @@ you should use the socket in the XDG_RUNTIME_DIR/colorshell.sock for a faster re
     private init(): void {
         // load gresource from build-defined path
         try {
-            this.#gresource = Gio.Resource.load(GRESOURCES_FILE.split('/').filter(s => 
+            const gresourcesPath: string = GRESOURCES_FILE.startsWith('/') ? GRESOURCES_FILE : (GRESOURCES_FILE.split('/').filter(s => 
                 s !== ""
             ).map(path => {
                 // support environment variables at runtime
@@ -179,9 +179,9 @@ you should use the socket in the XDG_RUNTIME_DIR/colorshell.sock for a faster re
 
                     return env;
                 }
-
                 return path;
             }).join('/'));
+            this.#gresource = Gio.Resource.load(gresourcesPath);
             Gio.resources_register(this.#gresource);
 
             // add icons