library: keep the artist screen fast and avoid placeholder labels

Rewrite the artist album lookup as indexed UNION branches instead of ORs
that scanned the song table, and let artistName take the first indexed row.

Keep the type label and album count blank until the album flow has emitted,
so the page no longer flashes "Artist" and "0 albums" before showing the
real values.

app/src/test/kotlin/com/subtracks/data/db/QueryTimingMeasurementTest.kt

@@ -91,6 +91,8 @@ class QueryTimingMeasurementTest {
         timed("albums first page (recent)") { dao.albumsByRecent(1, 0, "").firstPage() }
         timed("artists first page (name)") { dao.artistsByName(1, 0, "").firstPage() }
         timed("artists first page (frequent)") { dao.artistsByFrequent(1, 0, "").firstPage() }
+        timed("artist albums") { dao.albumsForArtist(1, "ar0").first() }
+        timed("artist name") { dao.artistName(1, "ar0").first() }
         timed("playlists first page (name)") { dao.playlistsByName(1, "").firstPage() }
         timed("albums deep page") { dao.albumsByName(1, 0, "").deepPage(1000) }
         timed("albums search FTS") { dao.albumsByName(1, 0, "Album 1").firstPage() }

app/src/test/kotlin/com/subtracks/ui/library/ArtistDetailScreenTest.kt

@@ -24,7 +24,8 @@ class ArtistDetailScreenTest {
     private fun render(
         artist: Artist?,
         artistName: String,
-        isAlbumArtist: Boolean,
+        isAlbumArtist: Boolean? = null,
+        albumsLoaded: Boolean = true,
     ) {
         composeRule.setContent {
             SubtracksTheme {
@@ -33,6 +34,7 @@ class ArtistDetailScreenTest {
                     artistName = artistName,
                     isAlbumArtist = isAlbumArtist,
                     albums = emptyList(),
+                    albumsLoaded = albumsLoaded,
                     art = null,
                     coverArt = { _, _ -> null },
                     onBack = {},
@@ -62,4 +64,17 @@ class ArtistDetailScreenTest {
         composeRule.onNodeWithText("Album artist").assertExists()
         composeRule.onNodeWithContentDescription("More options").assertExists()
     }
+
+    @Test
+    fun theTypeAndCountStayBlankUntilTheAlbumsLoad() {
+        render(
+            artist = Artist(sourceId = 1, id = "ar-1", name = "Radiohead", albumCount = 1, starred = null),
+            artistName = "Radiohead",
+            albumsLoaded = false,
+        )
+
+        composeRule.onNodeWithText("Artist").assertDoesNotExist()
+        composeRule.onNodeWithText("Album artist").assertDoesNotExist()
+        composeRule.onNodeWithText("0 albums").assertDoesNotExist()
+    }
 }