refactor: make Following sync outcome explicit

src/main.py

@@ -3785,6 +3785,7 @@ async def mutate_global_search_preview_subscription(
         )
     return JSONResponse({
         **result,
+        "following_synced": True,
         "following_revision": following["revision"],
         "following_count": len(following["items"]),
     })

tests/test_following_api.py

@@ -42,7 +42,12 @@ async def test_confirmed_watch_updates_account_following_collection(monkeypatch,
         following = await client.get("/api/v1/following")
 
     assert watched.status_code == 200
-    assert watched.json() == {"watching": True, "following_revision": 1, "following_count": 1}
+    assert watched.json() == {
+        "watching": True,
+        "following_synced": True,
+        "following_revision": 1,
+        "following_count": 1,
+    }
     assert following.status_code == 200
     assert following.headers["cache-control"] == "no-store"
     assert following.json() == {"revision": 1, "items": [{

tests/test_global_search.py

@@ -285,6 +285,7 @@ async def test_search_preview_subscription_mutation_revalidates_target_and_confi
     expected_count = 1 if watching else 0
     assert response.json() == {
         "watching": watching,
+        "following_synced": True,
         "following_revision": expected_count,
         "following_count": expected_count,
     }