Fix #522: SVG round trips keep hidden objects and data-* attributes

An SVG used as an animation rig lost its hidden alternates and their
rotation pivots: the exporter left hidden objects out (only hidden layers
could be kept), and the importer dropped data-* attributes.

- SVG export: hiddenLayers (on by default for document.save, as before)
  now keeps hidden objects too, each written display="none" on its own
  element (path, image, text or group). Exports still leave them out
  unless asked; the CLI's convert asks, as a conversion keeps the
  document.
- An object's own data: ObjectAttributes.data, the data-* attributes in
  order (ours, data-name and data-vc-*, aside). The importer keeps them on
  the objects and layers they belong to (at most 64 per element), the
  exporter writes them back, the native format saves them (missing in
  older files), and object.setProps {data: {key: value|null}} sets or
  removes them.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/vectorcraft-cli/src/main.rs

@@ -69,7 +69,8 @@ USAGE:
       Open IN (any readable format) and export OUT in the format its extension picks (see Writable
       formats). --artboard is 0-based, --range 1-based (\"1-3,5\"); a PDF gets every artboard
       unless one of them is given, EPS the bounds of the art, the other formats the first artboard.
-      Live effects are kept; --outline-text writes SVG text as paths.
+      Live effects are kept, and hidden layers and objects (written hidden in SVG and PSD), with
+      SVG's data-* attributes; --outline-text writes SVG text as paths.
 
   vectorcraft-cli info FILE
       Print a JSON summary: the import warnings (what didn't come in as it was, such as an EPS
@@ -177,12 +178,10 @@ fn convert(args: &[String]) -> Result<(), String> {
     let [input, output] = <[String; 2]>::try_from(files).map_err(|_| "convert needs IN and OUT")?;
     let mut h = Headless::new();
     h.call("app.open", json!({"path": input})).map_err(|e| format!("open {input}: {e}"))?;
-    let r = h
-        .call(
-            "engine.execute",
-            json!({"command": "document.export", "params": {"path": output, "scale": scale, "artboard": artboard, "range": range, "outlineText": outline_text}}),
-        )
-        .map_err(|e| format!("export {output}: {e}"))?;
+    // A conversion keeps hidden layers and objects, written hidden, where the format can (SVG,
+    // PSD).
+    let params = json!({"path": output, "scale": scale, "artboard": artboard, "range": range, "outlineText": outline_text, "hiddenLayers": true});
+    let r = h.call("engine.execute", json!({"command": "document.export", "params": params})).map_err(|e| format!("export {output}: {e}"))?;
     outln!("{r}");
     Ok(())
 }