Add branded app icon

Exbyte Depot icon: white cube glyph on a violet gradient rounded square
(src-tauri/app-icon.svg), regenerated all platform icons via tauri icon.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/app-icon.svg

@@ -0,0 +1,21 @@
+<svg width="1024" height="1024" viewBox="0 0 1024 1024" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0" stop-color="#9a8bf9"/>
+      <stop offset="1" stop-color="#5b49e6"/>
+    </linearGradient>
+    <radialGradient id="glow" cx="0.5" cy="0.36" r="0.72">
+      <stop offset="0" stop-color="#ffffff" stop-opacity="0.30"/>
+      <stop offset="1" stop-color="#ffffff" stop-opacity="0"/>
+    </radialGradient>
+  </defs>
+  <rect x="64" y="64" width="896" height="896" rx="224" fill="url(#bg)"/>
+  <rect x="64" y="64" width="896" height="896" rx="224" fill="url(#glow)"/>
+  <g transform="translate(232,236) scale(23.3)" fill="none" stroke="#ffffff" stroke-width="1.35" stroke-linejoin="round" stroke-linecap="round">
+    <path d="M12 2 3 7v10l9 5 9-5V7l-9-5Z"/>
+    <path d="m3 7 9 5 9-5M12 12v10"/>
+  </g>
+  <g transform="translate(232,236) scale(23.3)">
+    <path d="M12 2 3 7l9 5 9-5-9-5Z" fill="#ffffff" fill-opacity="0.16"/>
+  </g>
+</svg>

src-tauri/icons/android/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+  <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+  <background android:drawable="@color/ic_launcher_background"/>
+</adaptive-icon>

src-tauri/icons/android/values/ic_launcher_background.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+  <color name="ic_launcher_background">#fff</color>
+</resources>