feat: add SVG favicon with brand thermometer icon

web/favicon.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect x="12" y="3" width="8" height="20" rx="4" fill="#ea580c"/>
+  <circle cx="16" cy="25" r="6" fill="#ea580c"/>
+  <rect x="14" y="10" width="4" height="13" rx="2" fill="#fbbf24"/>
+  <circle cx="16" cy="25" r="4" fill="#fbbf24"/>
+</svg>

web/templates/layout.html

@@ -4,7 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>{{t "app.name"}} — {{.Title}}</title>
-  <link rel="icon" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'><text y='.9em' font-size='90'>🌡</text></svg>">
+  <link rel="icon" type="image/svg+xml" href="/assets/favicon.svg">
   <link rel="stylesheet" href="/assets/css/app.css">
   <script>
     window.HG = { lang: "{{.Lang}}" };