fix(ui): respect Plasma style and add app branding

- Preserve the platform-selected QtQuick style on Plasma
- Add the QtPotato desktop entry and bundled app icon
- Remove the empty-state open-file action

src/icons/dev.trivk.qtpotato.svg

@@ -0,0 +1,47 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="256" height="256" viewBox="0 0 256 256">
+  <defs>
+    <radialGradient id="skin" cx="0.38" cy="0.32" r="0.8">
+      <stop offset="0" stop-color="#f8d79e"/>
+      <stop offset="0.6" stop-color="#e8b06a"/>
+      <stop offset="1" stop-color="#c98a45"/>
+    </radialGradient>
+    <linearGradient id="badge" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#5ee06c"/>
+      <stop offset="1" stop-color="#2fa83f"/>
+    </linearGradient>
+    <linearGradient id="leaf" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0" stop-color="#6fe57b"/>
+      <stop offset="1" stop-color="#2fa83f"/>
+    </linearGradient>
+  </defs>
+
+  <!-- shadow -->
+  <ellipse cx="124" cy="228" rx="84" ry="9" fill="#000" opacity="0.18"/>
+
+  <!-- sprout -->
+  <path d="M136 66 C136 54 139 45 144 38" fill="none" stroke="#2f8f3a" stroke-width="5" stroke-linecap="round"/>
+  <path d="M141 50 C128 30 108 28 101 35 C110 50 128 56 141 50 Z" fill="url(#leaf)"/>
+  <path d="M143 42 C151 20 175 16 183 23 C175 41 158 48 143 42 Z" fill="url(#leaf)"/>
+
+  <!-- body -->
+  <path d="M58 104 C70 70 108 56 150 60 C196 64 226 98 222 142 C218 188 180 216 128 216 C78 216 38 190 36 150 C35 128 48 116 58 104 Z"
+        fill="url(#skin)" stroke="#a86a2e" stroke-width="3"/>
+
+  <!-- potato spots -->
+  <ellipse cx="182" cy="98" rx="6" ry="4" fill="#b8793a" opacity="0.55" transform="rotate(-20 182 98)"/>
+  <ellipse cx="70" cy="182" rx="5" ry="3.5" fill="#b8793a" opacity="0.5" transform="rotate(25 70 182)"/>
+  <ellipse cx="80" cy="96" rx="4" ry="3" fill="#b8793a" opacity="0.45"/>
+
+  <!-- face -->
+  <ellipse cx="82" cy="152" rx="13" ry="8" fill="#ff7f8a" opacity="0.5"/>
+  <ellipse cx="170" cy="152" rx="13" ry="8" fill="#ff7f8a" opacity="0.5"/>
+  <ellipse cx="100" cy="134" rx="9" ry="11.5" fill="#3b2414"/>
+  <ellipse cx="152" cy="134" rx="9" ry="11.5" fill="#3b2414"/>
+  <circle cx="103.5" cy="129" r="3.6" fill="#fff"/>
+  <circle cx="155.5" cy="129" r="3.6" fill="#fff"/>
+  <path d="M114 151 Q120 159 126 151 Q132 159 138 151" fill="none" stroke="#3b2414" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round"/>
+
+  <!-- play badge -->
+  <circle cx="200" cy="198" r="38" fill="url(#badge)" stroke="#fff8ee" stroke-width="6"/>
+  <path d="M189 180 L218 198 L189 216 Z" fill="#fff" stroke="#fff" stroke-width="7" stroke-linejoin="round"/>
+</svg>