allow queue loading during drag; keep the album title after a reorder

- the mid-drag load guard also stopped the window extending while
  auto-scrolling, so dragging a context row over a long up-next block hit
  the loaded edge and dropped. Removed it: loadOlder/loadNewer now extend
  from the min/max loaded position, which is what prevents the duplicates.
- a reordered track becomes an explicit song entry, so the context kind
  switches to Song and the queue title fell back to "Next from here".
  sourceName now resolves a song entry to its album so the title keeps
  the album name.

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

@@ -1001,6 +1001,25 @@ class PlaybackControllerTest {
         assertEquals(runBlocking { queues.combinedIndexOf(snapshot, "s3") }, controller.state.value.position)
     }
 
+    @Test
+    fun movingThePlayingContextTrackStillResolvesAnAlbumTitle() {
+        seedAlbum(3, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 1)
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        runBlocking { controller.move(1, 0) }
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        assertEquals("Album", runBlocking { controller.sourceTitle(controller.state.value.context) })
+    }
+
     @Test
     fun nextFollowsTheReorderedQueue() {
         seedAlbum(3, sourceId = 1)