[no bump] Move technical docs to docs/, add icon and PNG export tool

README now carries the icon, TL;DR, description and features; the
technical sections live in docs/. tools/icon_png.py renders
images/icon.svg to a square PNG (512x512 by default, --resolution N).
plugin.json points at the plugin's own icon.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

images/icon.svg

@@ -0,0 +1,40 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="640" height="640" viewBox="0 0 640 640">
+  <defs>
+    <linearGradient id="bg" x1="0.3" y1="0" x2="0.7" y2="1">
+      <stop offset="0" stop-color="#F89B2E"/><stop offset="0.5" stop-color="#F7724A"/><stop offset="1" stop-color="#F5517A"/>
+    </linearGradient>
+    <radialGradient id="glow" cx="0.5" cy="0.45" r="0.5">
+      <stop offset="0" stop-color="#FF5A3C" stop-opacity="0.18"/><stop offset="1" stop-color="#FF5A3C" stop-opacity="0"/>
+    </radialGradient>
+    <linearGradient id="paper" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#F7F7F7"/><stop offset="1" stop-color="#E2E2E2"/>
+    </linearGradient>
+    <linearGradient id="star" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#FFE27A"/><stop offset="1" stop-color="#FFC53D"/>
+    </linearGradient>
+    <linearGradient id="sky" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#7CC8FF"/><stop offset="1" stop-color="#CFEBFF"/>
+    </linearGradient>
+    <linearGradient id="metal" x1="0" y1="0" x2="1" y2="0">
+      <stop offset="0" stop-color="#9C9C9C"/><stop offset="0.45" stop-color="#E4E4E4"/><stop offset="1" stop-color="#A8A8A8"/>
+    </linearGradient>
+    <clipPath id="photo"><rect x="166" y="196" width="228" height="208" rx="18"/></clipPath>
+    <filter id="sh" x="-20%" y="-20%" width="140%" height="150%">
+      <feDropShadow dx="0" dy="10" stdDeviation="10" flood-color="#7A1E2E" flood-opacity="0.28"/>
+    </filter>
+  </defs>
+  <rect width="640" height="640" fill="url(#bg)"/>
+  <rect width="640" height="640" fill="url(#glow)"/>
+
+  <g transform="translate(-22,-6)">
+    <rect filter="url(#sh)" x="180" y="140" width="280" height="260" rx="34" transform="rotate(8 320 270)" fill="#FFFFFF" fill-opacity="0.45" stroke="#FFFFFF" stroke-opacity="0.7" stroke-width="5"/>
+    <rect filter="url(#sh)" x="140" y="170" width="280" height="260" rx="34" fill="url(#paper)" stroke="#B9B9B9" stroke-width="6" stroke-linejoin="round"/>
+    <g clip-path="url(#photo)">
+      <rect x="166" y="196" width="228" height="208" fill="url(#sky)"/>
+      <circle cx="340" cy="248" r="24" fill="#FFD34E"/>
+      <path d="M150,410 L238,296 L290,360 L328,318 L410,410 Z" fill="#4DBB7E"/>
+      <path d="M238,296 L262,327 L246,322 L232,338 L222,317 Z" fill="#FFFFFF" fill-opacity="0.8"/>
+    </g>
+    <path filter="url(#sh)" fill="url(#star)" stroke="#F59A2E" stroke-width="8" stroke-linejoin="round" d="M352,482 C352,404 398,370 470,368 V326 L556,402 L470,478 V436 C420,434 384,446 352,482 Z"/>
+  </g>
+</svg>