feat: load optional XDG TOML configuration with session overrides

Checks/system-playback.swift

@@ -1,5 +1,6 @@
 import AppKit
 import MediaPlayer
+import TerebiConfiguration
 
 @main
 @MainActor
@@ -29,13 +30,20 @@ struct SystemPlaybackChecks {
                 "buffer readout can be enabled before playback and reveals controls")
         initialModel.shutdown()
         let restoredModel = PlayerModel(defaults: defaults)
-        require(restoredModel.showsBufferInfo, "enabled buffer readout survives model recreation")
-        restoredModel.setShowsBufferInfo(false)
-        require(!restoredModel.showsBufferInfo, "buffer readout can be explicitly disabled")
+        require(!restoredModel.showsBufferInfo, "session opt-in does not survive model recreation")
         restoredModel.shutdown()
+        let configuredModel = PlayerModel(defaults: defaults, configuration:
+            PlayerConfiguration(showBufferInfo: true, automaticQuality: true, snapToEdges: false))
+        require(configuredModel.showsBufferInfo && configuredModel.automaticYouTubeQuality
+                && !configuredModel.compactWindow.snappingEnabled, "configuration initializes all three controls")
+        configuredModel.setShowsBufferInfo(false)
+        configuredModel.setAutomaticYouTubeQuality(false)
+        configuredModel.compactWindow.snappingEnabled = true
+        configuredModel.shutdown()
         let model = PlayerModel(defaults: defaults)
         defer { model.shutdown() }
-        require(!model.showsBufferInfo, "explicitly disabled buffer readout survives model recreation")
+        require(!model.showsBufferInfo && !model.automaticYouTubeQuality && model.compactWindow.snappingEnabled,
+                "session overrides never replace built-in settings")
         model.setVolume(0)
         let directory = URL(fileURLWithPath: CommandLine.arguments[1], isDirectory: true)
         let center = MPNowPlayingInfoCenter.default()