mcp, cli: list each command's parameters as JSON Schema

CommandSpec::listing gives id, label, the parameter doc and the schema; MCP
list_commands, the control channel's engine.commands and the new
fieldcraft-cli commands --json use it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/control.rs

@@ -174,9 +174,7 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
             let Some(steps) = p.get("commands") else { return err("missing `commands` (a list of {command, params})") };
             wrap(app.run_script(steps).map(|()| json!({"journal": app.session.journal.len()})))
         }
-        "engine.commands" => {
-            ok(Value::Array(fieldcraft_engine::commands().iter().map(|c| json!({"id": c.id, "label": c.label, "params": c.params})).collect()))
-        }
+        "engine.commands" => ok(Value::Array(fieldcraft_engine::commands().iter().map(fieldcraft_engine::CommandSpec::listing).collect())),
         "ui.inspect" => ok(json!({
             "ui": app.ui,
             "camera": app.cam,