Various fixes for desktop (#4976)

# Description of Changes
- ~Force classic logo~
- Refer to email instead of username in SaaS sign in flow
- Allow drag-and-drop files into desktop app
- Convert terminology & icons from upload/download to open/save in
desktop version

frontend/src/core/components/shared/FilePickerModal.tsx

@@ -16,6 +16,7 @@ import {
 import PictureAsPdfIcon from '@mui/icons-material/PictureAsPdf';
 import { useTranslation } from 'react-i18next';
 import { FileId } from '@app/types/file';
+import { useFileActionTerminology } from '@app/hooks/useFileActionTerminology';
 
 interface FilePickerModalProps {
   opened: boolean;
@@ -31,6 +32,7 @@ const FilePickerModal = ({
   onSelectFiles,
 }: FilePickerModalProps) => {
   const { t } = useTranslation();
+  const terminology = useFileActionTerminology();
   const [selectedFileIds, setSelectedFileIds] = useState<FileId[]>([]);
 
   // Reset selection when modal opens
@@ -130,7 +132,7 @@ const FilePickerModal = ({
       <Stack gap="md">
         {storedFiles.length === 0 ? (
           <Text c="dimmed" ta="center" py="xl">
-            {t("fileUpload.noFilesInStorage", "No files available in storage. Upload some files first.")}
+            {terminology.noFilesInStorage}
           </Text>
         ) : (
           <>
@@ -253,7 +255,7 @@ const FilePickerModal = ({
             disabled={selectedFileIds.length === 0}
           >
             {selectedFileIds.length > 0
-              ? `${t("fileUpload.loadFromStorage", "Load")} ${selectedFileIds.length} ${t("fileUpload.uploadFiles", "Files")}`
+              ? `${t("fileUpload.loadFromStorage", "Load")} ${selectedFileIds.length} ${terminology.uploadFiles}`
               : t("fileUpload.loadFromStorage", "Load Files")
             }
           </Button>

frontend/src/core/components/shared/LandingPage.tsx

@@ -8,6 +8,8 @@ import { useFilesModalContext } from '@app/contexts/FilesModalContext';
 import { BASE_PATH } from '@app/constants/app';
 import { useLogoPath } from '@app/hooks/useLogoPath';
 import { useFileManager } from '@app/hooks/useFileManager';
+import { useFileActionTerminology } from '@app/hooks/useFileActionTerminology';
+import { useFileActionIcons } from '@app/hooks/useFileActionIcons';
 
 const LandingPage = () => {
   const { addFiles } = useFileHandler();
@@ -19,6 +21,8 @@ const LandingPage = () => {
   const logoPath = useLogoPath();
   const { loadRecentFiles } = useFileManager();
   const [hasRecents, setHasRecents] = React.useState<boolean>(false);
+  const terminology = useFileActionTerminology();
+  const icons = useFileActionIcons();
 
   const handleFileDrop = async (files: File[]) => {
     await addFiles(files);
@@ -187,10 +191,10 @@ const LandingPage = () => {
                     onClick={handleNativeUploadClick}
                     onMouseEnter={() => setIsUploadHover(true)}
                   >
-                    <LocalIcon icon="upload" width="1.25rem" height="1.25rem" style={{ color: 'var(--accent-interactive)' }} />
+                    <LocalIcon icon={icons.uploadIconName} width="1.25rem" height="1.25rem" style={{ color: 'var(--accent-interactive)' }} />
                     {isUploadHover && (
                       <span style={{ marginLeft: '.5rem' }}>
-                        {t('landing.uploadFromComputer', 'Upload from computer')}
+                        {terminology.uploadFromComputer}
                       </span>
                     )}
                   </Button>
@@ -239,7 +243,7 @@ const LandingPage = () => {
             className="text-[var(--accent-interactive)]"
             style={{ fontSize: '.8rem' }}
           >
-            {t('fileUpload.dropFilesHere', 'Drop files here or click the upload button')}
+            {terminology.dropFilesHere}
           </span>
         </div>
       </Dropzone>

frontend/src/core/components/shared/RightRail.tsx

@@ -6,6 +6,8 @@ import { useRightRail } from '@app/contexts/RightRailContext';
 import { useFileState, useFileSelection } from '@app/contexts/FileContext';
 import { useNavigationState } from '@app/contexts/NavigationContext';
 import { useTranslation } from 'react-i18next';
+import { useFileActionTerminology } from '@app/hooks/useFileActionTerminology';
+import { useFileActionIcons } from '@app/hooks/useFileActionIcons';
 
 import LanguageSelector from '@app/components/shared/LanguageSelector';
 import { useRainbowThemeContext } from '@app/components/shared/RainbowThemeProvider';
@@ -44,6 +46,8 @@ export default function RightRail() {
   const { sidebarRefs } = useSidebarContext();
   const { position: tooltipPosition, offset: tooltipOffset } = useRightRailTooltipSide(sidebarRefs);
   const { t } = useTranslation();
+  const terminology = useFileActionTerminology();
+  const icons = useFileActionIcons();
   const viewerContext = React.useContext(ViewerContext);
   const { toggleTheme, themeMode } = useRainbowThemeContext();
   const { buttons, actions, allButtonsDisabled } = useRightRail();
@@ -165,9 +169,9 @@ export default function RightRail() {
       return t('rightRail.exportAll', 'Export PDF');
     }
     if (selectedCount > 0) {
-      return t('rightRail.downloadSelected', 'Download Selected Files');
+      return terminology.downloadSelected;
     }
-    return t('rightRail.downloadAll', 'Download All');
+    return terminology.downloadAll;
   }, [currentView, selectedCount, t]);
 
   return (
@@ -232,7 +236,7 @@ export default function RightRail() {
                 (currentView === 'viewer' ? !exportState?.canExport : totalItems === 0 || allButtonsDisabled)
               }
             >
-              <LocalIcon icon="download" width="1.5rem" height="1.5rem" />
+              <LocalIcon icon={icons.downloadIconName} width="1.5rem" height="1.5rem" />
             </ActionIcon>,
             downloadTooltip,
             tooltipPosition,