chore(ui): flip texture horizontally

src/shader/pixelbuf.vert

@@ -2,7 +2,7 @@
 out vec2 uv;
 
 const vec2 pos[3] = vec2[3](vec2(-1.0f, -1.0f), vec2(-1.0f, 3.0f), vec2(3.0f, -1.0f));
-const vec2 uvs[3] = vec2[3](vec2( 2.0f,  2.0f), vec2( 2.0f, 0.0f), vec2(0.0f,  2.0f));
+const vec2 uvs[3] = vec2[3](vec2( 0.0f,  2.0f), vec2( 0.0f, 0.0f), vec2(2.0f,  2.0f));
 
 void main() {
 	uv = uvs[gl_VertexID];