Coming back to the feed shows it as it was left

Leaving the feed keeps it in Services/FeedMemory.cs (posts, waiting posts, cursors and scroll; ten minutes, for the same
feed of the same persona), so coming back from a thread or a profile shows it again at once, older pages included,
instead of reading it anew; newer posts come behind the "new" button and through the stream as before.
tests/e2e FeedMemoryTests goes to a thread and back without a new read of the home timeline; the whole suite passes
(123, 5 skipped).

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

Program.cs

@@ -40,6 +40,7 @@ builder.Services.AddOptions()
 	.AddScoped<RequestStats>()
 	.AddScoped<AuthService>()
 	.AddScoped<TimelineService>()
+	.AddScoped<FeedMemory>()
 	.AddScoped<StatusService>()
 	.AddScoped<AccountService>()
 	.AddScoped<PortabilityService>()