Complete Ole2Frame: embed a picture file from a script

EmbedPicture builds the frame with OCS's own EmbeddedImage and
build_embedded_ole, so the opaque storage is never scripted. PNG, JPEG and
BMP are stored as read and other formats are re-encoded as PNG. The lifecycle
test now creates through Python; a new test covers formats, aspect, origin,
layer and refusals.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ipc/v4/protocol.rs

@@ -115,6 +115,7 @@ mod tests {
             },
             SolidOperation::Transform { handle: acadrust::Handle::new(7), matrix: [1.0; 16] },
             SolidOperation::RegionFromProfile { source: acadrust::Handle::new(3), layer: None, delete_source: true },
+            SolidOperation::EmbedPicture { path: "p.png".into(), origin: [0.0; 3], width: 5.0, layer: None },
             SolidOperation::Boolean {
                 first: acadrust::Handle::new(1),
                 second: acadrust::Handle::new(2),