SubscriptionService held one provider per backend and each resolved its
instance from settingsManager.subscriptionAccount, falling back to "the
first enabled Invidious instance" when that was unset. With several logins
possible on one instance that model breaks twice: two accounts would share
a single in-memory subscription cache, and the fallback could send an
account's request to a server it holds no credential for.
Providers are now built per account and cached by account ID, and each
resolves its instance and credential from the account it was built for -
no fallback. The protocol's accountType becomes a DataContext, which is
what actually identifies a provider now.
Views that branched on "is the subscription account local" read the context
instead, and the settings picker writes both stores. Keeping the legacy
setting in step is deliberate for now: several views still read it, and
letting the two diverge would show one account in the UI while serving
another's data. The Phase 3 switcher removes the last readers.
Signing out discards the account's provider so its cached subscriptions
cannot be served after the account is gone.
Settings → Notifications → Manage Channels: wrap the tvOS NavigationLink
destination in TVSidebarDetailContainer(showsDismissButton: true) so the
no-subscriptions, error, and loading states all have a focusable Done.
Channels sidebar tab: lift the tvOS search field + View Options button
out of the loaded-channels branch and render it above every state. The
empty state previously had zero focusable elements, leaving the right
pane blank when swiping in from the sidebar.
Renames YatteeServerCredentialsManager → BasicAuthCredentialsManager so the
same Keychain-backed username/password storage can be reused for any instance
type that sits behind a reverse proxy requiring HTTP Basic Auth. Adds a
one-time migration that moves existing items from the legacy
'com.yattee.yatteeserver' Keychain service to 'com.yattee.basicauth',
preserving the iCloud-sync attribute. No behavior change for end users.
On tvOS, ContentUnavailableView inside a Group doesn't expand to fill
available space — it sizes to content and aligns top-leading. Add
.frame(maxWidth: .infinity, maxHeight: .infinity) to all instances
so they center correctly in their parent containers.
