feat: update favicon configuration and standardize site metadata icons

public/icon.svg

@@ -0,0 +1,29 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="ESPDocs">
+  <title>ESPDocs</title>
+  <defs>
+    <linearGradient id="g" x1="6" y1="58" x2="58" y2="6" gradientUnits="userSpaceOnUse">
+      <stop offset="0" stop-color="#3b82f6"/>
+      <stop offset="0.55" stop-color="#8b5cf6"/>
+      <stop offset="1" stop-color="#ec4899"/>
+    </linearGradient>
+  </defs>
+
+  <!-- Pinos entrando pela esquerda: o sinal que chega do silício. -->
+  <g stroke="url(#g)" stroke-width="3.4" stroke-linecap="round">
+    <path d="M2 21h7"/>
+    <path d="M2 32h7"/>
+    <path d="M2 43h7"/>
+  </g>
+
+  <!-- Corpo do encapsulamento. -->
+  <rect x="9.25" y="9.25" width="45.5" height="45.5" rx="13"
+        fill="none" stroke="url(#g)" stroke-width="4.5"/>
+
+  <!-- Os mesmos três níveis viram linhas de texto: a documentação.
+       Comprimento decrescente para ler como parágrafo. -->
+  <g stroke="url(#g)" stroke-width="4.5" stroke-linecap="round">
+    <path d="M19 21h26"/>
+    <path d="M19 32h21"/>
+    <path d="M19 43h15"/>
+  </g>
+</svg>