More efficient flat file list format and various UX improvements (#3)

This is a major upgrade with assorted things included.

- Navigation flows improved, search appears in URL history, cleared when navigating to another folder
- More efficient file list format for faster loads
- Efficient updates, never re-send full root another time (except at connection)
- Large number of watching and filelist updates (inotify issues remain)
- File size coloring
- Fixed ZIP generation random glitches (thread race condition)
- Code refactoring, cleanup, typing fixes
- More tests

frontend/src/components/SvgButton.vue

@@ -0,0 +1,42 @@
+<template>
+  <button class="action-button">
+    <component :is="icon" />
+    <slot></slot>
+  </button>
+</template>
+
+<script setup lang="ts">
+import { defineAsyncComponent, defineProps } from 'vue'
+
+const props = defineProps<{
+  name: string
+}>()
+
+const icon = defineAsyncComponent(() => import(`@/assets/svg/${props.name}.svg`))
+</script>
+
+<style>
+.action-button {
+  background: none;
+  border: none;
+  color: #ccc;
+  cursor: pointer;
+  transition: all 0.2s ease;
+  padding: 0.2em;
+  width: 3em;
+  height: 3em;
+}
+.action-button:hover,
+.action-button:focus {
+  color: #fff;
+  transform: scale(1.1);
+}
+svg {
+  fill: #ccc;
+  transform: fill 0.2s ease;
+}
+.action-button:hover svg,
+.action-button:focus svg {
+  fill: #fff;
+}
+</style>