gate the library on playback restore so the bottom bar lands in place

The tab bar was laid out before playback was known, so the restored mini player arrived
later and re-laid the whole bottom area: a couple of frames of bump, and the mini player
"loading in" after the library. SubtracksRoot now waits for PlaybackController to finish
connecting and restoring (a `ready` flag, set after restore or on disconnect) before it
composes the library, so the first library frame already includes the mini player and
nothing moves.

With playback resolved up front, the `restored` flag and its special enter/inset specs
are pointless, so they are reverted; playback the user starts animates as before.

app/src/test/kotlin/com/subtracks/playback/PlaybackControllerTest.kt

@@ -28,6 +28,7 @@ import okhttp3.OkHttpClient
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
@@ -161,17 +162,16 @@ class PlaybackControllerTest {
     }
 
     @Test
-    fun restoringMarksTheStateUntilPlaybackStarts() {
+    fun theReadyStateResolvesWithTheRestoredItemAlreadyInPlace() {
         seedAlbum(5, sourceId = 1)
         runBlocking { queues.replace(listOf(queues.albumEntry(1, "al1"))) }
 
+        assertFalse(controller.ready.value)
+
         controller.connect()
-        await { handle.items.isNotEmpty() }
+        await { controller.ready.value }
 
-        assertTrue(controller.state.value.restored)
-
-        controller.playAlbum(1, "al1", 0)
-        await { !controller.state.value.restored }
+        assertNotNull("the mini player must be drawable once ready", controller.state.value.item)
     }
 
     @Test