Rename the project to FieldCraft

Crates fieldcraft-*, binaries fieldcraft and fieldcraft-cli, the .fieldcraft file (format tag
fieldcraft/1, manifest fieldcraft.json), FIELDCRAFT_* environment variables, the MCP server
name, egui widget ids (fc_*), the app icon document FieldCraft.icon and its generated family,
docs and licences. No compatibility shim: no files of the earlier name exist.

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

crates/engine/src/cmd/define.rs

@@ -2,11 +2,11 @@
 //! points, couplings, point masses, springs and dashpots, boundary conditions, loads, fluid
 //! domains and steps, and the step activity table.
 //!
-//! Each definition's parameters are its JSON form in the model (the same form a `.modelcraft`
+//! Each definition's parameters are its JSON form in the model (the same form a `.fieldcraft`
 //! file stores), plus its `name`. `create` fails when the name is taken, `edit` replaces an
 //! existing definition, `delete` refuses while another definition refers to it.
 
-use modelcraft_model::{
+use fieldcraft_model::{
     BoundaryCondition, Coupling, FaceCondition, FluidBoundary, FluidDomain, Load, Material, Model, PointMass, ReferencePoint, Section, Set, Spring,
     Step,
 };