packaging: add deb/flatpak build flow and desktop metadata

packaging/linux/io.orbithub.OrbitHub.svg

@@ -0,0 +1,20 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256">
+  <defs>
+    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" stop-color="#20354f"/>
+      <stop offset="100%" stop-color="#0b1524"/>
+    </linearGradient>
+    <linearGradient id="ring" x1="0%" y1="0%" x2="100%" y2="0%">
+      <stop offset="0%" stop-color="#69e2ff"/>
+      <stop offset="100%" stop-color="#7cf0a3"/>
+    </linearGradient>
+  </defs>
+
+  <rect x="18" y="24" width="220" height="152" rx="16" fill="url(#bg)" stroke="#94a3b8" stroke-opacity="0.4"/>
+  <rect x="32" y="38" width="192" height="112" rx="8" fill="#101b2e"/>
+  <rect x="96" y="182" width="64" height="16" rx="8" fill="#3a4a63"/>
+  <rect x="70" y="200" width="116" height="14" rx="7" fill="#52627c"/>
+
+  <ellipse cx="128" cy="98" rx="74" ry="24" fill="none" stroke="url(#ring)" stroke-width="11" transform="rotate(-14 128 98)"/>
+  <circle cx="128" cy="98" r="18" fill="#8be4ff"/>
+</svg>