Keep one login's verdicts and content off another's

A feed failure recorded its verdict before checking whether anyone was
still waiting for it, and the verdict resolves the *currently* selected
account — so a 401 from a credential the app had already moved off could
mark its replacement, or a different account, as rejected indefinitely.

The instance browser drops its feed, subscriptions and playlists when
the selected login changes. Nothing else there would notice: the
instance, the tab and the "already has data" shortcut are all unchanged
between two accounts on the same server.

Caches are no longer discarded while the identity is unresolved. With
iCloud Drive off the scope drops to unresolved on every activation and
comes back the same, and the context reads as local in between — which
looked like a move and threw the caches away several times a day.

Local is always in the account picker again. Its feed needs a Yattee
Server and reports that itself; with correction no longer moving away
from local, leaving it out of the list made it unreachable once left.
And the subscriptions view reloads when an instance is switched off,
which moves reads to local without touching the context or any status.

Yattee/Services/Subscriptions/SubscriptionAccountValidator.swift

@@ -74,13 +74,11 @@ final class SubscriptionAccountValidator {
     var availableAccounts: [SubscriptionAccount] {
         var accounts: [SubscriptionAccount] = []
 
-        // Add local if Yattee Server is configured and enabled
-        let hasYatteeServer = instancesManager.instances.contains {
-            $0.type == .yatteeServer && $0.isEnabled
-        }
-        if hasYatteeServer {
-            accounts.append(.local)
-        }
+        // Local is always offered. Its *feed* needs a Yattee Server and says so
+        // itself when there is none; that is not a reason to make the user's
+        // own data unselectable — and since correction no longer moves away
+        // from local, leaving it out would make it unreachable once left.
+        accounts.append(.local)
 
         // Add logged-in and enabled Invidious instances
         for instance in instancesManager.instances {