Update DroidDeck branding to split D mark (#37)

artwork/README.md

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+# DroidDeck mark
+
+`droiddeck-mark.svg` is the editable source for the split-D mark. The blue orb is `#1A9FFF`; its halo and the two separator bars are transparent cutouts. The bars are centered on x=63.97, the endpoint of the curved half in the original Steam Deck symbol, and use the halo's 15.83-unit thickness. The mark is optically centered in its view box with a small rightward offset to balance its asymmetric silhouette.
+
+Android currently consumes raster resources for the launcher layers and the Compose logo. The `mipmap-*/ic_launcher_foreground.png` files are density-sized exports of the SVG, with the mark kept inside the adaptive icon safe area. The matching backgrounds are white. `drawable-nodpi/logo.png` composes the same mark on a white circular badge for use on the app's dark surfaces.

artwork/droiddeck-mark.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="-55.98 0 239.92 223.72" role="img" aria-labelledby="title">
+  <title id="title">DroidDeck split D with a circular orb halo and solid blue orb</title>
+  <defs>
+    <mask id="negative-space" maskUnits="userSpaceOnUse" x="-31.98" y="0" width="207.92" height="223.72">
+      <rect x="-31.98" y="0" width="207.92" height="223.72" fill="#fff"/>
+      <circle cx="63.98" cy="111.86" r="71.81" fill="#000"/>
+      <rect x="56.055" y="0" width="15.83" height="45" fill="#000"/>
+      <rect x="56.055" y="178.72" width="15.83" height="45" fill="#000"/>
+    </mask>
+  </defs>
+  <path fill="#1b1b1b" mask="url(#negative-space)" d="M-31.98 0H63.97c61.84 0 111.96 50.08 111.96 111.86S125.81 223.72 63.97 223.72H-31.98V0Z"/>
+  <circle cx="63.98" cy="111.86" r="55.98" fill="#1A9FFF"/>
+</svg>