Let the sidebar's channels and playlists follow the data context

Yattee/Services/Subscriptions/InvidiousSubscriptionProvider.swift

@@ -139,6 +139,10 @@ final class InvidiousSubscriptionProvider: SubscriptionProvider {
         cachePopulated ? cachedChannels.count : nil
     }
 
+    var cachedSubscriptions: [Channel]? {
+        cachePopulated ? cachedChannels : nil
+    }
+
     // MARK: - Private Helpers
 
     /// Gets the authenticated Invidious instance and session ID from account settings.

Yattee/Services/Subscriptions/LocalSubscriptionProvider.swift

@@ -26,7 +26,12 @@ final class LocalSubscriptionProvider: SubscriptionProvider {
     // MARK: - SubscriptionProvider
 
     func fetchSubscriptions() async throws -> [Channel] {
-        // Convert Subscription models to Channel models
+        subscriptionChannels()
+    }
+
+    /// Converts Subscription models to Channel models, synchronously — the
+    /// store is local, so there is nothing to await.
+    private func subscriptionChannels() -> [Channel] {
         dataManager.subscriptions().map { subscription in
             Channel(
                 id: ChannelID(source: subscription.contentSource, channelID: subscription.channelID),
@@ -67,4 +72,9 @@ final class LocalSubscriptionProvider: SubscriptionProvider {
     var cachedSubscriptionCount: Int? {
         dataManager.subscriptionCount
     }
+
+    var cachedSubscriptions: [Channel]? {
+        // Local data needs no cache warm-up — the store is always readable.
+        subscriptionChannels()
+    }
 }

Yattee/Services/Subscriptions/PipedSubscriptionProvider.swift

@@ -139,6 +139,10 @@ final class PipedSubscriptionProvider: SubscriptionProvider {
         cachePopulated ? cachedChannels.count : nil
     }
 
+    var cachedSubscriptions: [Channel]? {
+        cachePopulated ? cachedChannels : nil
+    }
+
     // MARK: - Private Helpers
 
     /// Gets the authenticated Piped instance and auth token from account settings.

Yattee/Services/Subscriptions/SubscriptionProvider.swift

@@ -40,6 +40,10 @@ protocol SubscriptionProvider: Sendable {
     /// Returns nil when the provider hasn't populated its cache yet.
     var cachedSubscriptionCount: Int? { get }
 
+    /// The subscribed channels known without a network fetch.
+    /// Returns nil when the provider hasn't populated its cache yet.
+    var cachedSubscriptions: [Channel]? { get }
+
     /// Refreshes the local cache of subscriptions from the remote source.
     /// For local provider, this is a no-op.
     func refreshCache() async throws