geometry: read tagged meshes through the VFS, refuse singular transforms, share the model's coordinate limit (#6)

read_3mf_file reads through solidcraft_io::vfs like open_design_file (regular files only,
browser files too), so the engine drops its own capped reader and EngineError::File.
A build item whose transform flattens its object is an error, and coordinates use
modelcraft_model::MAX_COORD (1e9) instead of a looser limit of their own.


Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/lib.rs

@@ -26,9 +26,6 @@ pub enum EngineError {
     Model(#[from] modelcraft_model::Error),
     #[error(transparent)]
     Geometry(#[from] modelcraft_geometry::Error),
-    /// A file could not be read or written.
-    #[error("{0}")]
-    File(String),
     /// A command panicked; the model is unchanged.
     #[error("internal error in {command}: {message}")]
     Internal { command: String, message: String },