add color updates to timer for feedback

src/roast.css

@@ -15,6 +15,24 @@ body {
     margin: 0;
 }
 
+/* Roast phase backgrounds */
+#timer.initial-phase {
+    background-color: #ffffff; /* white before Charge */
+}
+
+#timer.charge-phase {
+    background-color: #e6ffe6; /* pale green after Charge */
+}
+
+#timer.yellow-phase {
+    background-color: #fffdd0; /* light yellow after Yellow */
+}
+
+/* Dynamic muddy yellow-brown transition (0–40% dev) */
+#timer.dev-phase {
+    transition: background-color 0.5s ease;
+}
+
 #create-plan {
     padding: 20px;
     text-align: center;