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/fem/src/beam.rs

@@ -39,7 +39,7 @@
 //!   webs or the two flanges of a box) (W. D. Pilkey, *Analysis and Design of Elastic Beams*,
 //!   Wiley 2002, ch. 6).
 
-use modelcraft_model::{BeamProfile, Elastic};
+use fieldcraft_model::{BeamProfile, Elastic};
 
 use crate::dense::Matrix;
 use crate::dof::{DofSet, ElementDofs};
@@ -211,7 +211,7 @@ fn line_axis(xyz: &[[f64; 3]]) -> Result<(Vec3, f64)> {
     let [a, b] = xyz else {
         return Err(Error::Invalid(format!("a two-node line element has 2 nodes, got {}", xyz.len())));
     };
-    modelcraft_model::check_coordinates(xyz.as_flattened()).map_err(|e| Error::Invalid(e.to_string()))?;
+    fieldcraft_model::check_coordinates(xyz.as_flattened()).map_err(|e| Error::Invalid(e.to_string()))?;
     let d = sub(*b, *a);
     let length = norm(d);
     let ex = unit(d).ok_or_else(|| Error::Degenerate("a line element has zero length".into()))?;