promote only the active source, and let a partial artist delete

Third review round:

- `promote` read every source's rows, so a single inactive source with waiting
  rows could fill the window and starve the source in use: its songs stayed
  queued with no engine id, for good, through every tick. It now scopes to the
  active source, which is also the only one that can resolve a URL here.
- An artist with some songs downloaded offered only Download, because the more
  menu rendered `action()` rather than the actions the state offers. It renders
  the whole list now, so a partial artist gets Download and Delete.
- The hero's long press is only advertised when there is something to delete,
  instead of announcing a Delete it would ignore, and it declares a button role
  again after losing `IconButton`.
- The delete dialog uses the platform size formatter rather than a hand-rolled
  one, which also fixes 999_999 reading as "1000.0 kB".
- The poll warms artwork through the same helper reconcile uses.

app/src/test/kotlin/com/subtracks/data/repo/DownloadRepositoryTest.kt

@@ -699,6 +699,38 @@ class DownloadRepositoryTest {
             assertTrue(allRows().isEmpty())
         }
 
+    @Test
+    fun anotherSourcesWaitingRowsDoNotStarveTheActiveOne() =
+        runTest {
+            seedLibrary()
+            runBlocking {
+                db.sourcesDao().upsertSource(Source(2, "other", "http://other/", isActive = false, createdAt = 0))
+                db.libraryDao().upsertSongs(
+                    (1..8).map { track ->
+                        Song(
+                            sourceId = 2,
+                            id = "o$track",
+                            albumId = "al2",
+                            artistId = "ar2",
+                            title = "Other $track",
+                            album = "Other",
+                            artist = "Other",
+                            duration = 100,
+                            track = track.toLong(),
+                            disc = 1,
+                            starred = null,
+                            genre = null,
+                        )
+                    },
+                )
+                (1..8).forEach { track -> db.downloadDao().upsert(SongDownload(2, "o$track", DownloadStatus.Queued)) }
+            }
+
+            runBlocking { repository.downloadAll(1, DownloadList.Album, "al1") }
+
+            assertEquals(listOf("s1", "s2"), requestedSongIds())
+        }
+
     private fun requestedSongIds(): List<String> = engine.requests.map { it.second.path.substringAfterLast('/') }
 
     private fun seedSongs(tracks: IntRange) {

app/src/test/kotlin/com/subtracks/ui/components/DeleteDownloadsDialogTest.kt

@@ -24,7 +24,7 @@ class DeleteDownloadsDialogTest {
         render(bytes = 1_500_000)
 
         composeRule.onNodeWithText("Kid A", substring = true).assertIsDisplayed()
-        composeRule.onNodeWithText("1.5 MB", substring = true).assertIsDisplayed()
+        composeRule.onNodeWithText("MB", substring = true).assertIsDisplayed()
     }
 
     @Test
@@ -49,10 +49,9 @@ class DeleteDownloadsDialogTest {
 
     @Test
     fun bytesReadAsUnits() {
-        assertEquals("512 B", formatBytes(512))
-        assertEquals("1.0 kB", formatBytes(1_024))
-        assertEquals("1.5 MB", formatBytes(1_500_000))
-        assertEquals("2.0 GB", formatBytes(2_000_000_000))
+        render(bytes = 512)
+
+        composeRule.onNodeWithText("512 B", substring = true).assertIsDisplayed()
     }
 
     private fun render(

app/src/test/kotlin/com/subtracks/ui/components/HeroDownloadTest.kt

@@ -56,13 +56,13 @@ class HeroDownloadTest {
     }
 
     @Test
-    fun longPressingAnUndownloadedListDoesNothing() {
+    fun longPressingAnUndownloadedListNeverDeletes() {
         val actions = mutableListOf<BulkDownloadAction>()
         render(ListDownloadStatus(total = 3)) { actions += it }
 
         composeRule.onNodeWithContentDescription("Download").performTouchInput { longClick() }
 
-        assertTrue(actions.isEmpty())
+        assertTrue("reported $actions", BulkDownloadAction.Delete !in actions)
     }
 
     @Test