feat(app): add drag-and-drop file upload and file picker to composer (#1474)

- Desktop web: drag-and-drop non-image files onto the chat pane to upload
- Desktop web: file picker option in the composer attachment sheet
- Uploaded files are sent to the LLM as filename references in a tmp directory
- New useFilePicker hook for cross-platform file picking
- Extended useFileDropZone to support generic file drops
- Added UploadedFileAttachment type to protocol and composer attachment system
- Fixed adaptive modal sheet closing on backdrop press in selection mode

packages/app/src/i18n/resources/ar.ts

@@ -99,12 +99,15 @@ export const ar: TranslationResources = {
     },
     attachments: {
       addImage: "أضف صورة",
+      addFile: "Upload file",
       addIssueOrPr: "أضف مشكلة أو PR",
       dropImagesHere: "إسقاط الصور هنا",
+      dropFilesHere: "Drop files here",
       editQueuedMessage: "تحرير الرسالة في قائمة الانتظار",
       sendQueuedMessageNow: "إرسال رسالة في قائمة الانتظار الآن",
       openImage: "فتح مرفق الصورة",
       removeImage: "إزالة مرفق الصورة",
+      removeFile: "Remove file attachment",
       openGithub: "افتح{{kind}}#{{number}}",
       removeGithub: "إزالة{{kind}}#{{number}}",
       browserElement: "العنصر ·{{tag}}",
@@ -119,6 +122,8 @@ export const ar: TranslationResources = {
       noHostSelected: "لم يتم تحديد مضيف",
       initialPromptRequired: "مطلوب موجه الأولي",
       alreadyLoading: "جارٍ التحميل بالفعل",
+      uploadFailed: "Failed to upload file",
+      fileTooLarge: "{{fileName}} is too large (max {{size}})",
     },
     clientCommands: {
       archiveAgent: "أرشفة الوكيل الحالي",