Remove dead code found by Periphery on all platforms

Delete declarations that Periphery reports unused on every platform that
compiles them (iOS, macOS, tvOS), including nine views used only by their
own previews. Platform-gated code still used on another platform, device-
only MPV render paths, migration models, CloudKit record names, App
Intents metadata and unused parameters are kept.

Yattee/Data/DataManager+ChannelNotificationSettings.swift

@@ -131,41 +131,6 @@ extension DataManager {
         save()
     }
 
-    /// Deletes notification settings for a channel.
-    /// - Parameter channelID: The channel ID to delete settings for.
-    func deleteNotificationSettings(for channelID: String) {
-        let descriptor = FetchDescriptor<ChannelNotificationSettings>(
-            predicate: #Predicate { $0.channelID == channelID }
-        )
-
-        do {
-            let results = try modelContext.fetch(descriptor)
-            guard !results.isEmpty else { return }
-
-            // Capture scopes before deleting
-            let scopes = results.map {
-                SourceScope.from(
-                    sourceRawValue: $0.sourceRawValue,
-                    globalProvider: $0.globalProvider,
-                    instanceURLString: $0.instanceURLString,
-                    externalExtractor: nil
-                )
-            }
-
-            for settings in results {
-                modelContext.delete(settings)
-            }
-            save()
-
-            // Queue scoped CloudKit deletions
-            for scope in scopes {
-                cloudKitSync?.queueChannelNotificationSettingsDelete(channelID: channelID, scope: scope)
-            }
-        } catch {
-            LoggingService.shared.logCloudKitError("Failed to delete notification settings", error: error)
-        }
-    }
-
     /// Inserts or updates notification settings from CloudKit sync.
     /// - Parameter settings: The notification settings to upsert.
     func upsertChannelNotificationSettings(_ settings: ChannelNotificationSettings) {