fix(mobile/upload): activities now appear in browser after upload; reconcile synced_at on fresh server

Three bugs fixed:
- /api/upload/bas and /api/upload/raw never updated user_dir/index.json, so
  merge_all couldn't include uploaded activities in year shards — they existed
  on disk but were invisible to the browser feed. Fixed by _upsert_index_summary()
  called before merge_all().
- Silent catch {} in uploadLocalActivities swallowed all per-activity errors;
  replaced with console.warn so failures are visible in Expo logs.
- After a server wipe, synced_at flags on the device caused "Nothing to upload"
  forever. uploadFeed() now reconciles against GET /api/feed at the start of each
  upload: local activities not found on the server get synced_at cleared.

Also: live upload progress ("Uploading N / M…"), failed count in result message,
onProgress callback on uploadFeed(), countPendingUploads() helper.

mobile/app/(tabs)/index.tsx

@@ -53,14 +53,19 @@ export default function FeedScreen() {
   const doUpload = useCallback(async () => {
     setUploading(true);
     setStatusMsg(null);
-    const result = await uploadFeed(db);
+    const result = await uploadFeed(db, (n, total) => {
+      setStatusMsg({ ok: true, text: `Uploading ${n} / ${total}…` });
+    });
     setUploading(false);
     if (result.error) {
       showMsg(false, result.error);
-    } else if (!result.uploaded) {
+    } else if (!result.uploaded && !result.failed) {
       showMsg(true, 'Nothing to upload');
     } else {
-      showMsg(true, `Uploaded ${result.uploaded} activit${result.uploaded === 1 ? 'y' : 'ies'}`);
+      const parts: string[] = [];
+      if (result.uploaded) parts.push(`${result.uploaded} uploaded`);
+      if (result.failed)   parts.push(`${result.failed} failed`);
+      showMsg(result.failed ? false : true, parts.join(', '));
     }
   }, [db]);