Reference Picker: Drag-and-drop badges

- Make badges draggable with the mouse
  - Replace Insert and Replace modes with a single Apply action
  - Add a hint for the keyboard shortcut
  - Reorganize directory structure

services/web/modules/reference-picker/frontend/js/extensions/reference-picker-keybinding.ts

@@ -0,0 +1,60 @@
+import { EditorView, keymap, showTooltip, type Tooltip } from '@codemirror/view'
+import { Prec, StateEffect, StateField, type Extension } from '@codemirror/state'
+import { startCompletion } from '@codemirror/autocomplete'
+import { getBibkeyArgumentNode } from '@/features/source-editor/utils/tree-operations/ancestors'
+
+export const setCitationHint = StateEffect.define<Tooltip | null>()
+
+export const citationHint = StateField.define<Tooltip | null>({
+  create: () => null,
+  update(value, transaction) {
+    for (const effect of transaction.effects) {
+      if (effect.is(setCitationHint)) return effect.value
+    }
+    return transaction.docChanged ||
+      !transaction.state.selection.eq(transaction.startState.selection)
+      ? null
+      : value
+  },
+  provide: field => showTooltip.from(field),
+})
+
+export function citationRange(view: EditorView) {
+  const { doc, selection } = view.state
+  const pos = selection.main.head
+  const node = getBibkeyArgumentNode(view.state, pos)
+  if (!node) return null
+
+  const from = node.from + 1
+  const to = node.to - 1
+  if (
+    pos < from || pos > to ||
+    doc.sliceString(node.from, from) !== '{' ||
+    doc.sliceString(to, node.to) !== '}'
+  ) return null
+
+  return { braceFrom: from, braceTo: to }
+}
+
+function openPickerIfInCite(view: EditorView): boolean {
+  try {
+    const range = citationRange(view)
+    if (range) {
+      window.dispatchEvent(new CustomEvent('reference:openPicker', { detail: range }))
+      return true
+    }
+  } catch {
+    // Fall back to ordinary completion during parser recovery.
+  }
+  return startCompletion(view)
+}
+
+export const extension = (): Extension => [
+  citationHint,
+  Prec.highest(
+    keymap.of([
+      { key: 'Ctrl-Space', run: openPickerIfInCite },
+      { key: 'Alt-Space', run: startCompletion },
+    ])
+  ),
+]