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/lib.rs

@@ -1,7 +1,7 @@
-//! Finite element kernels shared by ModelCraft's structural solvers.
+//! Finite element kernels shared by FieldCraft's structural solvers.
 //!
 //! Pure functions over element geometry and material constants, with no solver loop and no
-//! global state, so the implicit solver (`modelcraft-solver`) and the explicit solver that follows
+//! global state, so the implicit solver (`fieldcraft-solver`) and the explicit solver that follows
 //! it use the same element technology:
 //! - [`dof`]: degree-of-freedom kinds, what elements declare, and the global numbering
 //!   ([`DofLayout`]) every solver assembles on;