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/scripts/toc.inline.ts

@@ -1,4 +1,3 @@
-const bufferPx = 150
 const observer = new IntersectionObserver((entries) => {
   for (const entry of entries) {
     const slug = entry.target.id
@@ -28,7 +27,6 @@ function toggleToc(this: HTMLElement) {
 function setupToc() {
   const toc = document.getElementById("toc")
   if (toc) {
-    const collapsed = toc.classList.contains("collapsed")
     const content = toc.nextElementSibling as HTMLElement | undefined
     if (!content) return
     toc.addEventListener("click", toggleToc)