perf(explorer): client side explorer (#1810)

* start work on client side explorer

* fix tests

* fmt

* generic test flag

* add prenav hook

* add highlight class

* make flex more consistent, remove transition

* open folders that are prefixes of current path

* make mobile look nice

* more style fixes

quartz/components/OverflowList.tsx

@@ -0,0 +1,39 @@
+import { JSX } from "preact"
+
+const OverflowList = ({
+  children,
+  ...props
+}: JSX.HTMLAttributes<HTMLUListElement> & { id: string }) => {
+  return (
+    <ul class="overflow" {...props}>
+      {children}
+      <li class="overflow-end" />
+    </ul>
+  )
+}
+
+OverflowList.afterDOMLoaded = (id: string) => `
+document.addEventListener("nav", (e) => {
+  const observer = new IntersectionObserver((entries) => {
+    for (const entry of entries) {
+      const parentUl = entry.target.parentElement
+      if (entry.isIntersecting) {
+        parentUl.classList.remove("gradient-active")
+      } else {
+        parentUl.classList.add("gradient-active")
+      }
+    }
+  })
+
+  const ul = document.getElementById("${id}")
+  if (!ul) return
+
+  const end = ul.querySelector(".overflow-end")
+  if (!end) return
+
+  observer.observe(end)
+  window.addCleanup(() => observer.disconnect())
+})
+`
+
+export default OverflowList