Follow requests asked again, and followed accounts found by name

A server can take a Follow with 202 and drop it afterwards, as Pleroma does
while it cannot fetch our actor; the request then stayed pending for good.
Following again now sends an unanswered request once more, the same
activity, at most once an hour (a delivery's `again` key).

accounts/search takes following=true: only accounts the persona follows,
by the start of their name, display name or server, never resolved; a
client fills a list with it. "already take" becomes "already taken".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub.Tests/Http/MastodonListsTests.cs

@@ -142,6 +142,21 @@ namespace PrivaPub.Tests.Http
 			Assert.Contains(fromBob, (await alice.Client.Get("/api/v1/timelines/home")).Ok().Ids);
 		}
 
+		[Fact]
+		public async Task Account_search_with_following_finds_only_followed_accounts()
+		{
+			var alice = await _host.Mastodon("alice");
+			var prefix = $"ls{Guid.NewGuid():N}"[..10];
+			var followed = await _host.Mastodon(prefix + "a");
+			var stranger = await _host.Mastodon(prefix + "b");
+			await Follow(alice, followed);
+
+			var found = (await alice.Client.Get($"/api/v1/accounts/search?q={prefix}&following=true")).Ok().Ids.ToList();
+			Assert.Equal(new[] { followed.Id }, found);
+			Assert.Contains(stranger.Id, (await alice.Client.Get($"/api/v1/accounts/search?q={prefix}")).Ok().Ids);
+			Assert.Empty((await stranger.Client.Get($"/api/v1/accounts/search?q={prefix}&following=true")).Ok().Array);
+		}
+
 		[Fact]
 		public async Task An_unfollowed_account_leaves_the_personas_lists_and_does_not_come_back_with_a_new_follow()
 		{