docs: add light theme toggle

docs/faq.html

@@ -8,6 +8,12 @@
     <meta property="og:title" content="Pi Web FAQ" />
     <meta property="og:image" content="assets/pi-web-banner.png" />
     <link rel="icon" href="data:," />
+    <script>
+      (() => {
+        const theme = window.localStorage.getItem("pi-web-theme");
+        if (theme === "light" || theme === "dark") document.documentElement.dataset.theme = theme;
+      })();
+    </script>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link
@@ -24,7 +30,19 @@
           <a href="./">Home</a>
           <a href="install.html">Install</a>
           <a href="faq.html" aria-current="page">FAQ</a>
-          <a href="https://github.com/jmfederico/pi-web">GitHub</a>
+          <a class="github-link" href="https://github.com/jmfederico/pi-web" aria-label="Pi Web on GitHub">
+            <svg class="github-icon" viewBox="0 0 16 16" aria-hidden="true">
+              <path
+                fill="currentColor"
+                d="M8 0C3.58 0 0 3.67 0 8.2c0 3.63 2.29 6.7 5.47 7.79.4.08.55-.18.55-.4 0-.2-.01-.85-.01-1.55-2.01.38-2.53-.5-2.69-.96-.09-.24-.48-.96-.82-1.16-.28-.16-.68-.56-.01-.57.63-.01 1.08.59 1.23.84.72 1.24 1.87.89 2.33.68.07-.53.28-.89.51-1.09-1.78-.21-3.64-.91-3.64-4.04 0-.89.31-1.62.82-2.2-.08-.2-.36-1.03.08-2.16 0 0 .67-.22 2.2.84A7.4 7.4 0 0 1 8 3.94c.68 0 1.36.09 2 .28 1.53-1.06 2.2-.84 2.2-.84.44 1.13.16 1.96.08 2.16.51.58.82 1.31.82 2.2 0 3.14-1.87 3.83-3.65 4.04.29.26.54.76.54 1.53 0 1.1-.01 1.99-.01 2.27 0 .22.15.49.55.4A8.12 8.12 0 0 0 16 8.2C16 3.67 12.42 0 8 0Z"
+              />
+            </svg>
+            <span>GitHub</span>
+          </a>
+          <button class="theme-toggle" type="button" data-theme-toggle aria-label="Toggle light and dark theme">
+            <span data-theme-icon aria-hidden="true">◐</span>
+            <span data-theme-label>Theme</span>
+          </button>
         </div>
       </nav>
     </header>