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/material.rs

@@ -10,7 +10,7 @@
 //! S₁₁ = 1/E₁, S₁₂ = −ν₁₂/E₁, S₁₃ = −ν₁₃/E₁, S₂₃ = −ν₂₃/E₂ (ν_ji/E_j = ν_ij/E_i), and
 //! 1/G on the shear diagonal.
 
-use modelcraft_model::Elastic;
+use fieldcraft_model::Elastic;
 
 use crate::dense::inverse3;
 use crate::{Error, Result};