Redesign session UX: progress ring, round markers, red theme

- Animated ring sweeps the timer edge in proportion to the current step
  (react-native-svg), matching the meditation-timer idiom
- Per-block round markers: circle = squeeze, square = push, X = quick
  flicks; small interleaved dots distinguish rest rounds from work rounds
- Stamena-style red theme throughout (bg, accent, splash, adaptive icon)
- Home screen legend teaching the shape vocabulary

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app.json

@@ -7,13 +7,13 @@
     "icon": "./assets/images/icon.png",
     "scheme": "kegel",
     "userInterfaceStyle": "dark",
-    "backgroundColor": "#0F1115",
+    "backgroundColor": "#160B0B",
     "ios": {
       "bundleIdentifier": "com.marcus.kegel"
     },
     "android": {
       "adaptiveIcon": {
-        "backgroundColor": "#0F1115",
+        "backgroundColor": "#160B0B",
         "foregroundImage": "./assets/images/android-icon-foreground.png",
         "monochromeImage": "./assets/images/android-icon-monochrome.png"
       },
@@ -25,7 +25,7 @@
       [
         "expo-splash-screen",
         {
-          "backgroundColor": "#0F1115",
+          "backgroundColor": "#160B0B",
           "image": "./assets/images/splash-icon.png",
           "imageWidth": 120
         }