[enh] theme/simple: custom router

Lay the foundation for loading scripts granularly depending on the endpoint it's
on.

Remove vendor specific prefixes as there are now managed by browserslist and
LightningCSS.

Enabled quite a few rules in Biome that don't come in recommended to better
catch issues and improve consistency.

Related:

- https://github.com/searxng/searxng/pull/5073#discussion_r2256037965
- https://github.com/searxng/searxng/pull/5073#discussion_r2256057100

client/simple/src/js/main/autocomplete.ts

@@ -0,0 +1,129 @@
+import { assertElement, http, listen, settings } from "../core/toolkit.ts";
+
+const fetchResults = async (qInput: HTMLInputElement, query: string): Promise<void> => {
+  try {
+    let res: Response;
+
+    if (settings.method === "GET") {
+      res = await http("GET", `./autocompleter?q=${query}`);
+    } else {
+      res = await http("POST", "./autocompleter", { body: new URLSearchParams({ q: query }) });
+    }
+
+    const results = await res.json();
+
+    const autocomplete = document.querySelector<HTMLElement>(".autocomplete");
+    assertElement(autocomplete);
+
+    const autocompleteList = document.querySelector<HTMLUListElement>(".autocomplete ul");
+    assertElement(autocompleteList);
+
+    autocomplete.classList.add("open");
+    autocompleteList.replaceChildren();
+
+    // show an error message that no result was found
+    if (results?.[1]?.length === 0) {
+      const noItemFoundMessage = Object.assign(document.createElement("li"), {
+        className: "no-item-found",
+        textContent: settings.translations?.no_item_found ?? "No results found"
+      });
+      autocompleteList.append(noItemFoundMessage);
+      return;
+    }
+
+    const fragment = new DocumentFragment();
+
+    for (const result of results[1]) {
+      const li = Object.assign(document.createElement("li"), { textContent: result });
+
+      listen("mousedown", li, () => {
+        qInput.value = result;
+
+        const form = document.querySelector<HTMLFormElement>("#search");
+        form?.submit();
+
+        autocomplete.classList.remove("open");
+      });
+
+      fragment.append(li);
+    }
+
+    autocompleteList.append(fragment);
+  } catch (error) {
+    console.error("Error fetching autocomplete results:", error);
+  }
+};
+
+const qInput = document.getElementById("q") as HTMLInputElement | null;
+assertElement(qInput);
+
+let timeoutId: number;
+
+listen("input", qInput, () => {
+  clearTimeout(timeoutId);
+
+  const query = qInput.value;
+  const minLength = settings.autocomplete_min ?? 2;
+
+  if (query.length < minLength) return;
+
+  timeoutId = window.setTimeout(async () => {
+    if (query === qInput.value) {
+      await fetchResults(qInput, query);
+    }
+  }, 300);
+});
+
+const autocomplete: HTMLElement | null = document.querySelector<HTMLElement>(".autocomplete");
+const autocompleteList: HTMLUListElement | null = document.querySelector<HTMLUListElement>(".autocomplete ul");
+if (autocompleteList) {
+  listen("keyup", qInput, (event: KeyboardEvent) => {
+    const listItems = [...autocompleteList.children] as HTMLElement[];
+
+    const currentIndex = listItems.findIndex((item) => item.classList.contains("active"));
+    let newCurrentIndex = -1;
+
+    switch (event.key) {
+      case "ArrowUp": {
+        const currentItem = listItems[currentIndex];
+        if (currentItem && currentIndex >= 0) {
+          currentItem.classList.remove("active");
+        }
+        // we need to add listItems.length to the index calculation here because the JavaScript modulos
+        // operator doesn't work with negative numbers
+        newCurrentIndex = (currentIndex - 1 + listItems.length) % listItems.length;
+        break;
+      }
+      case "ArrowDown": {
+        const currentItem = listItems[currentIndex];
+        if (currentItem && currentIndex >= 0) {
+          currentItem.classList.remove("active");
+        }
+        newCurrentIndex = (currentIndex + 1) % listItems.length;
+        break;
+      }
+      case "Tab":
+      case "Enter":
+        if (autocomplete) {
+          autocomplete.classList.remove("open");
+        }
+        break;
+      default:
+        break;
+    }
+
+    if (newCurrentIndex !== -1) {
+      const selectedItem = listItems[newCurrentIndex];
+      if (selectedItem) {
+        selectedItem.classList.add("active");
+
+        if (!selectedItem.classList.contains("no-item-found")) {
+          const qInput = document.getElementById("q") as HTMLInputElement | null;
+          if (qInput) {
+            qInput.value = selectedItem.textContent ?? "";
+          }
+        }
+      }
+    }
+  });
+}