fix(save): preserve 3D view and thumbnails

Persist camera, render state, and solid fallback geometry across saves. Generate previews from a clean live viewport and refresh recent-file thumbnails immediately.

src/scene/convert/solid3d_tess.rs

@@ -42,6 +42,8 @@ pub(crate) fn body_transform(
             values.extend_from_slice(&components[..len]);
         } else if let Some(value) = token.as_float() {
             values.push(value);
+        } else if let Some(value) = token.as_integer() {
+            values.push(value as f64);
         } else if let Some(text) = token.as_string() {
             for word in text.split_ascii_whitespace() {
                 let Ok(value) = word.parse::<f64>() else {