Implement the reviewed UI icon system and durable review workflow (#853)

Thanks @Nathan-Dane.

crates/engine/src/cmd/plastic.rs

@@ -21,7 +21,7 @@ pub static COMMANDS: &[CommandSpec] = &[
     CommandSpec::new("plastic.lip", "Lip", lip).at("PLASTIC", "CREATE").icon("lip").params(
         "face: [x,y,z] on the rim face of a shelled body; width, height; type?: lip|groove; gap? (groove clearance); side?: inside|outside (which rim edge); body?",
     ),
-    CommandSpec::new("plastic.snap_fit", "Snap Fit", snap_fit).at("PLASTIC", "CREATE").icon("snap").params(
+    CommandSpec::new("plastic.snap_fit", "Snap Fit", snap_fit).at("PLASTIC", "CREATE").icon("snap_fit").params(
         "position: [x,y,z] on a face; direction? (default: out of the face); hook: [x,y,z] (the catch's direction); length, thickness, width, catch_depth, catch_length; body?",
     ),
     CommandSpec::new("plastic.rest", "Rest", rest).at("PLASTIC", "CREATE").icon("rest").params(
@@ -36,7 +36,7 @@ pub static COMMANDS: &[CommandSpec] = &[
     CommandSpec::new("plastic.assign_rule", "Assign Plastic Rule", assign_rule).at("PLASTIC", "SETUP").icon("plastic_assign").params(
         "bodies: [names]; rule: name (empty: no rule) — plastic features on these bodies take its draft and clearance as defaults",
     ),
-    CommandSpec::new("plastic.rules", "List Plastic Rules", list_rules).noundo().params("→ rules with their expressions and values, the active rule and the rules assigned to bodies"),
+    CommandSpec::new("plastic.rules", "List Plastic Rules", list_rules).icon("plastic_rule").noundo().params("→ rules with their expressions and values, the active rule and the rules assigned to bodies"),
 ];
 
 fn rule_json(s: &Session, r: &PlasticRule) -> Value {