Phase 6.4: DMS-Forms on RHF + Zod

- Dms.tsx folder-create: RHF+Zod (name required)
- ShareDialog add-share: RHF+Zod (shareId required, shareType/permission kept as useState)
- Error display under each field
- Preserved all existing functionality: folder tree, file grid, share links
- Added 2 validation tests for ShareDialog (empty shareId, valid submit)

frontend/src/pages/Dms.tsx

@@ -7,6 +7,9 @@
 
 import React, { useState, useEffect, useCallback, useRef } from 'react';
 import { useTranslation } from 'react-i18next';
+import { useForm } from 'react-hook-form';
+import { zodResolver } from '@hookform/resolvers/zod';
+import { z } from 'zod';
 import { Link } from 'react-router-dom';
 import { Button } from '@/components/ui/Button';
 import { Input } from '@/components/ui/Input';
@@ -69,7 +72,6 @@ export function DmsPage() {
   // Modal state
   const [showUpload, setShowUpload] = useState(false);
   const [showNewFolder, setShowNewFolder] = useState(false);
-  const [newFolderName, setNewFolderName] = useState('');
   const [previewFile, setPreviewFile] = useState<DmsFile | null>(null);
   const [shareFile, setShareFile] = useState<DmsFile | null>(null);
   const [deleteTarget, setDeleteTarget] = useState<DmsFile | null>(null);
@@ -77,6 +79,17 @@ export function DmsPage() {
   const [showBulkMove, setShowBulkMove] = useState(false);
   const [bulkMoveTarget, setBulkMoveTarget] = useState<string>('');
 
+  // ── Folder create form (RHF + Zod) ──
+  const folderSchema = z.object({
+    name: z.string().min(1, 'required'),
+  });
+  type FolderFormData = z.infer<typeof folderSchema>;
+
+  const { register: registerFolder, handleSubmit: handleSubmitFolder, reset: resetFolder, formState: { errors: folderErrors } } = useForm<FolderFormData>({
+    resolver: zodResolver(folderSchema),
+    defaultValues: { name: '' },
+  });
+
   // Mobile view state
   const [activeView, setActiveView] = useState<'tree' | 'files' | 'details'>('tree');
 
@@ -236,16 +249,15 @@ export function DmsPage() {
   }, [deleteTarget, selectedFile, toast, t]);
 
   // Handle create folder
-  const handleCreateFolder = useCallback(async () => {
-    if (!newFolderName.trim()) return;
+  const handleCreateFolder = useCallback(async (data: FolderFormData) => {
     setSubmittingFolder(true);
     try {
       const folder = await createFolder({
-        name: newFolderName.trim(),
+        name: data.name.trim(),
         parent_id: selectedFolderId,
       });
       setFolders((prev) => [...prev, folder]);
-      setNewFolderName('');
+      resetFolder({ name: '' });
       setShowNewFolder(false);
       toast.success(t('dms.createFolder'));
     } catch (err) {
@@ -253,7 +265,7 @@ export function DmsPage() {
       toast.error(msg);
     }
     setSubmittingFolder(false);
-  }, [newFolderName, selectedFolderId, toast, t]);
+  }, [selectedFolderId, toast, t, resetFolder]);
 
   // Handle upload complete
   const handleUploadComplete = useCallback(() => {
@@ -469,25 +481,22 @@ export function DmsPage() {
 
       {/* New folder form */}
       {showNewFolder && (
-        <div className="mb-2 p-3 bg-secondary-50 border-b border-secondary-200" data-testid="new-folder-form">
+        <form onSubmit={handleSubmitFolder(handleCreateFolder)} className="mb-2 p-3 bg-secondary-50 border-b border-secondary-200" data-testid="new-folder-form">
           <div className="flex items-center gap-3 max-w-md">
             <Input
               label={t('dms.folderName')}
-              value={newFolderName}
-              onChange={(e) => setNewFolderName(e.target.value)}
+              {...registerFolder('name')}
+              error={folderErrors.name?.message === 'required' ? t('validation.required') : undefined}
               placeholder={t('dms.folderName')}
-              onKeyDown={(e) => {
-                if (e.key === 'Enter') handleCreateFolder();
-              }}
             />
-            <Button size="sm" onClick={handleCreateFolder} isLoading={submittingFolder}>
+            <Button size="sm" type="submit" isLoading={submittingFolder}>
               {t('dms.createFolder')}
             </Button>
-            <Button variant="secondary" size="sm" onClick={() => { setShowNewFolder(false); setNewFolderName(''); }}>
+            <Button variant="secondary" size="sm" type="button" onClick={() => { setShowNewFolder(false); resetFolder({ name: '' }); }}>
               {t('dms.cancel')}
             </Button>
           </div>
-        </div>
+        </form>
       )}
 
       {/* Upload dropzone */}