feat(phase-4-09): create new components — FolderRow, FolderBreadcrumb, FolderDeleteModal, ShareModal, DocumentPreviewModal, SearchBar, SortControls, AuditLogTab

- FolderRow: inline rename, three-dot menu, delete/rename callbacks, outside-click close
- FolderBreadcrumb: truncation at depth > 4, nav aria-label, ol structure
- FolderDeleteModal: role=dialog, warning icon, doc count in body, Keep/Delete buttons
- ShareModal: handle input, recipients list with revoke, 404/409 error handling
- DocumentPreviewModal: iframe with proxy URL only (never presigned), Escape/overlay close
- SearchBar: role=search, aria-label, Escape clears
- SortControls: aria-pressed, direction indicator, toggle vs switch logic
- AuditLogTab: filters, paginated table, CSV export via window.location.href
- api/client.js: add adminListAuditLog function

frontend/src/components/documents/DocumentPreviewModal.vue

@@ -0,0 +1,71 @@
+<template>
+  <!-- Overlay -->
+  <div
+    ref="overlayRef"
+    class="fixed inset-0 bg-black/60 z-50 flex flex-col"
+    role="dialog"
+    aria-modal="true"
+    aria-label="Document preview"
+    @click="handleOverlayClick"
+  >
+    <!-- Header bar -->
+    <div class="bg-white border-b border-gray-200 px-6 py-3 flex items-center justify-between shrink-0">
+      <span class="text-sm font-medium text-gray-900 truncate max-w-xs">{{ doc.filename || doc.original_name }}</span>
+      <button
+        @click="emit('close')"
+        aria-label="Close preview"
+        class="text-gray-400 hover:text-gray-600 transition-colors ml-4 shrink-0"
+      >
+        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12" />
+        </svg>
+      </button>
+    </div>
+
+    <!-- iframe content -->
+    <div class="flex-1 overflow-hidden">
+      <iframe
+        class="w-full h-full border-0"
+        :src="proxyUrl"
+        title="Document preview"
+      ></iframe>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, computed, onMounted, onUnmounted } from 'vue'
+
+const props = defineProps({
+  doc: {
+    type: Object,
+    required: true,
+  },
+})
+
+const emit = defineEmits(['close'])
+
+const overlayRef = ref(null)
+
+const proxyUrl = computed(() => `/api/documents/${props.doc.id}/content`)
+
+function handleOverlayClick(e) {
+  if (e.target === overlayRef.value) {
+    emit('close')
+  }
+}
+
+function handleKeydown(e) {
+  if (e.key === 'Escape') {
+    emit('close')
+  }
+}
+
+onMounted(() => {
+  document.addEventListener('keydown', handleKeydown)
+})
+
+onUnmounted(() => {
+  document.removeEventListener('keydown', handleKeydown)
+})
+</script>