add favicon

cmd/ingestd/web/favicon.svg

@@ -0,0 +1,12 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Weatherstation">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0" stop-color="#0f2b3d"/>
+      <stop offset="1" stop-color="#163b52"/>
+    </linearGradient>
+  </defs>
+  <rect width="64" height="64" rx="14" fill="url(#bg)"/>
+  <circle cx="20" cy="22" r="8" fill="#f4d35e"/>
+  <path d="M8 40 C16 34, 24 36, 30 30 C36 24, 44 24, 52 18" fill="none" stroke="#7bdff2" stroke-width="4" stroke-linecap="round"/>
+  <path d="M10 48 L18 40 L26 44 L34 34 L42 38 L54 26" fill="none" stroke="#f4b942" stroke-width="3" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>