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/styles/darkmode.scss

@@ -8,6 +8,7 @@
   height: 20px;
   margin: 0 10px;
   text-align: inherit;
+  flex-shrink: 0;
 
   & svg {
     position: absolute;