engine: read the files commands name through fieldcraft_io::fs

file.open, geometry.open, geometry.import.mesh and reopening a model's
geometry read through the io crate's file edge instead of SolidCraft's
vfs, so in the browser they see the files the page holds (the same
store saves write to). Natively it is the same capped regular-file read.
fieldcraft-geometry drops its path-based readers (read_file,
open_design_file, read_3mf_file): it works on bytes, and reading files
is the io crate's job.

Part of #119

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/geometry/src/design.rs

@@ -2,9 +2,8 @@
 //! with SolidCraft, and hand back its bodies with persistent face names.
 //!
 //! The design is rebuilt from its authoritative inputs (sketches, features, parameters); cached
-//! display meshes in the file are never used. [`open_design`] takes bytes; [`open_design_file`]
-//! reads a path through SolidCraft's file access, which in the browser is the in-memory files the
-//! web host loaded.
+//! display meshes in the file are never used. [`open_design`] takes the file's bytes (reading
+//! files is `fieldcraft_io::fs`'s job, which in the browser holds the page's files).
 
 use solidcraft_doc::{Document, Model, naming};
 use solidcraft_kernel::{KernelError, guard};
@@ -45,11 +44,6 @@ pub fn open_design(bytes: &[u8]) -> Result<Design> {
     rebuild(&doc)
 }
 
-/// Read a design file (a regular file of at most [`MAX_DESIGN_BYTES`]) and rebuild it.
-pub fn open_design_file(path: &str) -> Result<Design> {
-    open_design(&crate::read_file(path, MAX_DESIGN_BYTES)?)
-}
-
 /// Rebuild an in-memory document (the design half of [`open_design`]).
 pub(crate) fn rebuild(doc: &Document) -> Result<Design> {
     let model = guard("rebuild design", || {
@@ -165,8 +159,5 @@ mod tests {
             assert!(open_design(bytes).is_err(), "{bytes:?}");
         }
         assert!(open_design(&vec![b' '; MAX_DESIGN_BYTES + 1]).is_err());
-        for path in ["", "/", "/dev/zero", "/no/such/design.solidcraft"] {
-            assert!(open_design_file(path).is_err(), "{path}");
-        }
     }
 }