DMS redesign: 3-column explorer layout with toolbar, source tree, file details panel

- Add backend endpoints: GET /dms/files, GET /dms/folders/{id}/files
- New SourceTree component: sources (Meine Dateien, Geteilte Ordner, Externe Speicher)
- New FileExplorer component: 5 view modes (list, table, icons-sm/md/lg)
- New FileDetails component: right panel with file metadata and actions
- Rewrite Dms.tsx: PluginToolbar + 3-column ResizablePanel layout
- Update DmsFile type: size_bytes + uploaded_by (backward compat aliases)
- Add 60+ i18n keys for de/en

app/plugins/builtins/dms/routes.py

@@ -502,6 +502,84 @@ async def get_file(
     }
 
 
+@router.get("/files")
+async def list_all_files(
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(get_current_user),
+):
+    """List all non-deleted files for the current tenant."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+
+    result = await db.execute(
+        select(DmsFile).where(
+            DmsFile.tenant_id == tenant_id,
+            DmsFile.deleted_at.is_(None),
+        )
+    )
+    files = result.scalars().all()
+
+    return [
+        {
+            "id": str(f.id),
+            "name": f.name,
+            "folder_id": str(f.folder_id) if f.folder_id else None,
+            "uploaded_by": str(f.uploaded_by),
+            "mime_type": f.mime_type,
+            "size_bytes": f.size_bytes,
+            "deleted_at": None,
+            "created_at": f.created_at.isoformat() if f.created_at else None,
+            "updated_at": f.updated_at.isoformat() if f.updated_at else None,
+        }
+        for f in files
+    ]
+
+
+@router.get("/folders/{folder_id}/files")
+async def list_files_in_folder(
+    folder_id: str,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(get_current_user),
+):
+    """List all non-deleted files in a specific folder (non-recursive)."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    fid = _parse_uuid(folder_id, "folder_id")
+
+    # Validate folder exists
+    folder_result = await db.execute(
+        select(Folder).where(
+            Folder.id == fid,
+            Folder.tenant_id == tenant_id,
+            Folder.deleted_at.is_(None),
+        )
+    )
+    if folder_result.scalar_one_or_none() is None:
+        raise HTTPException(404, detail={"detail": "Folder not found", "code": "not_found"})
+
+    result = await db.execute(
+        select(DmsFile).where(
+            DmsFile.tenant_id == tenant_id,
+            DmsFile.folder_id == fid,
+            DmsFile.deleted_at.is_(None),
+        )
+    )
+    files = result.scalars().all()
+
+    return [
+        {
+            "id": str(f.id),
+            "name": f.name,
+            "folder_id": str(f.folder_id) if f.folder_id else None,
+            "uploaded_by": str(f.uploaded_by),
+            "mime_type": f.mime_type,
+            "size_bytes": f.size_bytes,
+            "deleted_at": None,
+            "created_at": f.created_at.isoformat() if f.created_at else None,
+            "updated_at": f.updated_at.isoformat() if f.updated_at else None,
+        }
+        for f in files
+    ]
+
+
 @router.patch("/files/{file_id}")
 async def update_file(
     file_id: str,