feat: add custom app icon and adjust medium widget to 2x4

Replace Expo placeholder icons with a custom checklist icon using the
app's color palette (cream, teal blue, terracotta). Change medium widget
from 4x2 to 2x4 with horizontal resize support.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/images/icon.svg

@@ -0,0 +1,30 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024" width="1024" height="1024">
+  <!-- Background -->
+  <rect width="1024" height="1024" rx="224" fill="#FFF8F0"/>
+
+  <!-- Subtle border -->
+  <rect x="8" y="8" width="1008" height="1008" rx="216" fill="none" stroke="#E5E7EB" stroke-width="4"/>
+
+  <!-- Checklist (centered, scaled up) -->
+  <g transform="translate(512, 512) scale(1.45) translate(-512, -512)">
+    <!-- Line 1 - completed (with checkmark) -->
+    <circle cx="310" cy="320" r="38" fill="none" stroke="#4A90A4" stroke-width="14"/>
+    <polyline points="286,320 304,342 338,298" fill="none" stroke="#4A90A4" stroke-width="14" stroke-linecap="round" stroke-linejoin="round"/>
+    <rect x="400" y="302" width="360" height="36" rx="18" fill="#4A90A4" opacity="0.3"/>
+
+    <!-- Line 2 - active -->
+    <circle cx="310" cy="480" r="38" fill="none" stroke="#4A90A4" stroke-width="14"/>
+    <rect x="400" y="462" width="300" height="36" rx="18" fill="#4A90A4" opacity="0.6"/>
+
+    <!-- Line 3 - active with priority dot -->
+    <circle cx="310" cy="640" r="38" fill="none" stroke="#4A90A4" stroke-width="14"/>
+    <rect x="400" y="622" width="240" height="36" rx="18" fill="#4A90A4" opacity="0.6"/>
+    <circle cx="670" cy="640" r="14" fill="#C17767"/>
+
+    <!-- Pencil accent (bottom right) -->
+    <g transform="translate(710, 560) rotate(-45)">
+      <rect x="0" y="0" width="20" height="160" rx="10" fill="#C17767"/>
+      <polygon points="0,160 20,160 10,186" fill="#C17767"/>
+    </g>
+  </g>
+</svg>