feat: all profile uploads through transferStore; delete legacy POST /api/uploads

Migrates the remaining 5 profile/space upload sites (CreateSpace, AccountPanel
avatar+banner, OverviewPanel icon+banner) to transferStore.startUpload with
tray:false. Space sites pass _instanceOrigin so uploads route to the space's
home instance.

Removes upload/uploadWithProgress from api.uploads (and their private
uploadFile/uploadFileWithProgress helpers); api.uploads.url is preserved for
GET-path URL building. Deletes the server-side POST /api/uploads handler and
the now-unused @fastify/multipart plugin registration. GET /api/uploads/:filename
remains intact.

packages/web/src/components/modals/CreateSpace.tsx

@@ -3,8 +3,9 @@ import { Modal } from '../ui/Modal';
 import { ImageCropModal } from '../ui/ImageCropModal';
 import { useSpaceStore } from '../../stores/spaceStore';
 import { useUIStore } from '../../stores/uiStore';
+import { useTransferStore } from '../../stores/transferStore';
 import { useNavigate } from 'react-router-dom';
-import { api } from '../../api/client';
+import { waitForTransferAttachment } from '../../utils/waitForTransfer';
 import { AVATAR_COLORS } from '@backspace/shared';
 import type { SpaceVisibility, AvatarColor } from '@backspace/shared';
 import { SPACE_GRADIENT_MAP, getSpaceGradient } from '../../utils/gradients';
@@ -60,8 +61,9 @@ export function CreateSpaceModal() {
     const file = new File([blob], 'icon.png', { type: 'image/png' });
     setUploadingIcon(true);
     try {
-      const attachment = await api.uploads.upload(file);
-      setIconFilename(attachment.filename);
+      const tid = await useTransferStore.getState().startUpload(file, { tray: false });
+      const { filename } = await waitForTransferAttachment(tid);
+      setIconFilename(filename);
     } catch {
       setError('Failed to upload icon');
       setIconPreview(null);