docs(renderer): fix misleading inverse-rotation comment

The comment claimed to show the inverse matrix but actually showed
the forward R(θ) matrix. Correct it to show both forward and inverse
forms, matching the code below.

Co-authored-by: DeepSeek V4 <deepseek@v4.ai>

Author: zachelnet

crates/koharu-app/src/renderer.rs

@@ -1079,9 +1079,9 @@ fn rotate_sprite_expand_top_left(src: &RgbaImage, angle_rad: f32) -> (RgbaImage,
         for x in 0..dst_w {
             let world_x = x as f32 + min_x;
             let world_y = y as f32 + min_y;
-            // Inverse of CSS-like rotate(theta):
-            // x' =  cos*x - sin*y
-            // y' =  sin*x + cos*y
+            // Inverse rotation R(-θ): map destination pixel back to source.
+            //   Forward R(θ):  x' =  cos·x - sin·y,  y' =  sin·x + cos·y
+            //   Inverse R(-θ): x  =  cos·x' + sin·y', y  = -sin·x' + cos·y'
             let src_x = cos * world_x + sin * world_y;
             let src_y = -sin * world_x + cos * world_y;
             dst.put_pixel(x, y, sample_bilinear_rgba(src, src_x, src_y));