Make the brand purple the accent color and exercise Done check

Populate the previously-empty AccentColor asset (iOS + watch) with the
logo purple — a deep shade in light mode, brightened for dark mode and
the watch's black background. The exercise Done check now uses that
accent color and the in-progress indicator reads as a neutral gray, on
both iPhone and Apple Watch.

Workouts/Assets.xcassets/AccentColor.colorset/Contents.json

@@ -1,6 +1,33 @@
 {
   "colors" : [
     {
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0.588",
+          "green" : "0.078",
+          "red" : "0.337"
+        }
+      },
+      "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0.922",
+          "green" : "0.388",
+          "red" : "0.659"
+        }
+      },
       "idiom" : "universal"
     }
   ],

Workouts/Views/Common/CheckboxStatus.swift

@@ -17,9 +17,9 @@ enum CheckboxStatus {
 
     var color: Color {
         switch self {
-        case .checked: .green
+        case .checked: .accentColor
         case .unchecked: .gray
-        case .intermediate: .yellow
+        case .intermediate: .gray
         case .cancelled: .red
         }
     }