Open .solidcraft designs: rebuild, persistent face names, geometry commands (#4)

* geometry: open .solidcraft designs, rebuild them and keep persistent face names

open_design(bytes) reads a design (container or JSON) with solidcraft-io, rebuilds its
timeline with solidcraft-doc and returns its bodies; each Shape carries SolidCraft's
persistent face names by B-rep face index, so a face keeps its name through a parameter
edit. sample::plate_design builds a parametric test plate in code.

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

* engine: geometry.open, geometry.bodies and geometry.tessellate

The session holds the open design (shared, restored on a failed command, journalled when
it changes). Hostile-params coverage includes non-files, missing files, oversized paths and
extreme tolerances against an open design.

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

* docs: opening SolidCraft designs in the architecture and roadmap

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

* geometry: open_design_file reads through SolidCraft's bounded file access; simplify

The engine's hand-rolled capped read is replaced by open_design_file, which uses
solidcraft_io::vfs::read (refuses non-regular files before opening, works on the browser's
in-memory files). Drops the duplicate size check, simplifies the sample sketch and the
design-change test in Session::execute.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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/Cargo.toml

@@ -10,6 +10,7 @@ workspace = true
 
 [dependencies]
 modelcraft-model = { workspace = true }
+modelcraft-geometry = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 thiserror = { workspace = true }