add language dropdown (#4716)

docs/css/language-dropdown.css

@@ -0,0 +1,57 @@
+/* Language dropdown: injected by language-dropdown.js into the sidebar
+   footer, to the right of Mintlify's theme selector. Mirrors the almond
+   theme pill's exact metrics (lg:h-7 desktop / 2.375rem mobile, rounded-full,
+   border-gray-200/70, dark:border-white/[0.07]) so the two controls read as
+   one family. */
+#language-switch {
+  margin-left: auto;
+  display: inline-flex;
+  align-items: center;
+}
+
+#language-switch select {
+  appearance: none;
+  -webkit-appearance: none;
+  background-color: transparent;
+  border: 1px solid rgb(229 231 235 / 0.7);
+  border-radius: 9999px;
+  color: rgb(107 114 128);
+  cursor: pointer;
+  font-size: 0.75rem;
+  line-height: 1rem;
+  height: 2.375rem;
+  padding: 0 1.375rem 0 0.75rem;
+  /* Chevron, drawn in the same gray as the label text. */
+  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%236b7280' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
+  background-repeat: no-repeat;
+  background-position: right 0.5rem center;
+  background-size: 0.7rem;
+  transition: border-color 0.2s;
+}
+
+@media (min-width: 1024px) {
+  #language-switch select {
+    height: 1.75rem;
+  }
+}
+
+#language-switch select:hover {
+  color: rgb(75 85 99);
+  border-color: rgb(229 231 235);
+}
+
+#language-switch select:focus-visible {
+  outline: 2px solid rgb(45 0 247 / 0.4);
+  outline-offset: 1px;
+}
+
+.dark #language-switch select {
+  border-color: rgb(255 255 255 / 0.07);
+  color: rgb(156 163 175);
+  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%239ca3af' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
+}
+
+.dark #language-switch select:hover {
+  color: rgb(209 213 219);
+  border-color: rgb(255 255 255 / 0.1);
+}

docs/language-dropdown.js

@@ -0,0 +1,77 @@
+// Language dropdown: a small Python/TypeScript switcher injected into the
+// sidebar footer, next to Mintlify's theme selector. Selecting the other
+// language navigates to that project's docs site; selecting the current
+// language is a no-op. Styling lives in css/language-dropdown.css.
+(function () {
+  if (typeof window === "undefined") return;
+
+  var CURRENT_LANGUAGE = "python";
+
+  // TODO: fastmcp-ts has no public docs site URL discoverable in either repo
+  // yet. Until it exists, point at the repo README (the same cross-link the
+  // welcome page uses), then replace with the real docs URL.
+  var TYPESCRIPT_DOCS_URL = "https://github.com/PrefectHQ/fastmcp-ts";
+  var PYTHON_DOCS_URL = "https://gofastmcp.com";
+
+  var URLS = { python: PYTHON_DOCS_URL, typescript: TYPESCRIPT_DOCS_URL };
+
+  function findThemeSelector() {
+    // Mintlify's sidebar-footer DOM is not a stable public API, so probe a
+    // few markers (almond theme first) and give up quietly if none match.
+    return (
+      document.querySelector("[data-theme-preference-switch]") ||
+      document.querySelector('[role="group"][aria-label="Theme preference"]')
+    );
+  }
+
+  function buildDropdown() {
+    var label = document.createElement("label");
+    label.id = "language-switch";
+
+    var select = document.createElement("select");
+    select.setAttribute("aria-label", "Switch documentation language");
+
+    [
+      ["python", "Python"],
+      ["typescript", "TypeScript"],
+    ].forEach(function (entry) {
+      var option = document.createElement("option");
+      option.value = entry[0];
+      option.textContent = entry[1];
+      if (entry[0] === CURRENT_LANGUAGE) option.selected = true;
+      select.appendChild(option);
+    });
+
+    select.addEventListener("change", function () {
+      if (select.value === CURRENT_LANGUAGE) return;
+      window.location.href = URLS[select.value];
+    });
+
+    label.appendChild(select);
+    return label;
+  }
+
+  function addDropdown() {
+    if (document.getElementById("language-switch")) return;
+    var theme = findThemeSelector();
+    if (!theme || !theme.parentElement) return;
+    // Insert after the theme pill; margin-left:auto floats it right.
+    theme.parentElement.insertBefore(buildDropdown(), theme.nextSibling);
+  }
+
+  function run() {
+    if (document.readyState === "loading") {
+      document.addEventListener("DOMContentLoaded", addDropdown);
+    } else {
+      addDropdown();
+    }
+  }
+
+  run();
+
+  // Mintlify re-renders the sidebar on client-side navigation; re-inject when
+  // the dropdown disappears.
+  new MutationObserver(function () {
+    if (!document.getElementById("language-switch")) addDropdown();
+  }).observe(document.body, { subtree: true, childList: true });
+})();