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/ui-egui/src/frame.rs

@@ -93,7 +93,7 @@ fn popup<R>(
     if !open {
         return None;
     }
-    let id = egui::Id::new(("mc_menu", key));
+    let id = egui::Id::new(("fc_menu", key));
     let shown =
         egui::Popup::new(id, ui.ctx().clone(), anchor, ui.layer_id()).kind(egui::PopupKind::Menu).open_bool(&mut open).close_behavior(close).show(
             |ui| {