Add mobile format toolbar, image picker and move-to dialog

- Markdown format commands shared by Ctrl+B/I/K and a toolbar above the
  soft keyboard on touch devices; bold and italic stack correctly
- Fit the app to the visual viewport so the keyboard does not cover the
  caret or the toolbar
- Insert images from the photo library or a file picker
- Move notes and folders with a folder picker from the file tree menu or
  the command palette
- Open the file tree menu with a long press on touch devices

web/src/app/viewport.ts

@@ -0,0 +1,19 @@
+// 软键盘弹出时，iOS Safari 与新版 Android Chrome 只缩小可视区域、页面高度不变，
+// 编辑器底部（光标、键盘上方的工具条）会被键盘挡住。把应用高度设为可视区域的高度。
+// 双指缩放也会改变可视区域，缩放时不调整
+export function trackVisualViewport(onShrink: () => void) {
+  const vv = window.visualViewport
+  if (!vv) return
+  let last = vv.height
+  const update = () => {
+    const height = vv.scale > 1.01 ? null : vv.height
+    document.documentElement.style.setProperty('--rm-app-height', height === null ? '100%' : `${height}px`)
+    // iOS 会把页面整体上推以露出输入位置，应用高度已经适配，推回原位
+    if (height !== null && vv.offsetTop > 0) window.scrollTo(0, 0)
+    if (height !== null && height < last) requestAnimationFrame(onShrink)
+    last = vv.height
+  }
+  vv.addEventListener('resize', update)
+  vv.addEventListener('scroll', update)
+  update()
+}