ui: command forms drawn from the parameter schema

The context panel's form shows typed fields instead of the JSON text: numbers
with the model's units, drop-downs of choices and of the model's sets,
materials, steps and bodies, checkboxes, vectors, groups and one-of variants
(a load's type switches its fields), lists of rows. Defaults are filled in,
required fields are marked, a value the schema finds wrong is noted under its
field, and OK waits while a field holds text that is not a value. The JSON
text stays as the Advanced view. fields.rs holds the generic widgets (row,
number, drop-down, text), adapted from SolidCraft's dialog rows.

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

crates/ui-egui/src/lib.rs

@@ -28,7 +28,9 @@ pub mod browser;
 pub mod capture;
 pub mod context;
 pub mod control;
+pub mod fields;
 pub mod files;
+pub mod form;
 pub mod frame;
 pub mod gpu;
 pub mod icons;
@@ -155,6 +157,8 @@ pub struct ParamsDialog {
     /// The parameters as JSON text.
     pub text: String,
     pub error: Option<String>,
+    /// The JSON text is shown instead of the typed fields.
+    pub advanced: bool,
 }
 
 /// A status bar message.
@@ -519,7 +523,9 @@ impl ModelApp {
     /// Open a command's parameter form with `params` filled in.
     pub fn open_form(&mut self, command: &str, params: Value) {
         if let Some(spec) = fieldcraft_engine::find_command(command) {
-            self.dialog = Some(ParamsDialog { command: spec.id, text: params.to_string(), error: None });
+            // The schema's defaults are filled in, so the form starts as the command would run.
+            let params = spec.form.map_or(params.clone(), |form| fieldcraft_engine::schema::prefill(form, &params));
+            self.dialog = Some(ParamsDialog { command: spec.id, text: params.to_string(), error: None, advanced: spec.form.is_none() });
         }
     }