feat(app,android,ios): a blurred poster where a title has no wide art

A title with no fanart, banner or backdrop drew its poster cropped to the
band's shape across the title page and the library's banner: a blown-up
slice of the middle of it, which read as broken. Now the poster is
squeezed to 64x36 and blurred once when it is fetched, the cache keeps
that wash, and it is stretched across the band. The library's banner
stands the sharp poster at its right over it. Android blurs the poster
it already had (Android 12 and later; older versions decode it tiny),
and iOS likewise.

METADATA.md also records the quality badges of the commit before.

android/app/src/main/java/io/narl/protonstream/ui/LibraryScreen.kt

@@ -628,13 +628,7 @@ private fun featured(titles: List<TitleRecord>, resumable: List<Resumable>): Tit
 private fun FeaturedBanner(title: TitleRecord, resume: Resumable?, onPlay: (Int) -> Unit, onOpen: () -> Unit) {
     val playlist = remember(title) { title.seasons.flatMap(SeasonRecord::episodes) }
     Box(Modifier.fillMaxWidth().aspectRatio(4f / 3f).clip(MaterialTheme.shapes.large)) {
-        RemoteArtwork(
-            title.backdropUrl ?: title.posterUrl,
-            title.displayName,
-            Modifier.fillMaxSize(),
-            fallback = title.thumbnailSource,
-            labelled = false,
-        )
+        Backdrop(title, Modifier.fillMaxSize())
         Box(
             Modifier.fillMaxSize().background(
                 Brush.verticalGradient(0.35f to Color.Transparent, 1f to Color.Black.copy(alpha = 0.85f)),

android/app/src/main/java/io/narl/protonstream/ui/RemoteArtwork.kt

@@ -24,6 +24,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.runtime.staticCompositionLocalOf
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.blur
 import androidx.compose.ui.graphics.Brush
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.ImageBitmap
@@ -34,6 +35,7 @@ import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
 import androidx.compose.ui.text.font.FontWeight
 import io.narl.protonstream.native.NativeRuntime
 import kotlinx.coroutines.Dispatchers
@@ -112,6 +114,29 @@ internal fun RemoteArtwork(
     }
 }
 
+/**
+ * A title's art across the top of a page: its backdrop, or with none, its
+ * poster as a wash of its own colours — decoded tiny and blurred, so it reads as
+ * the poster's light rather than a blown-up slice of it. The desktop's
+ * `Fit::Ambient`. Android 11 and older cannot blur; there the tiny decode,
+ * stretched, is what softens it.
+ */
+@Composable
+internal fun Backdrop(title: TitleRecord, modifier: Modifier = Modifier) {
+    val wash = title.backdropUrl == null && title.posterUrl != null
+    RemoteArtwork(
+        title.backdropUrl ?: title.posterUrl,
+        title.displayName,
+        if (wash) modifier.blur(WASH_BLUR) else modifier,
+        fallback = title.thumbnailSource,
+        labelled = false,
+        maxEdge = if (wash) WASH_EDGE else null,
+    )
+}
+
+private val WASH_EDGE = 48.dp
+private val WASH_BLUR = 24.dp
+
 /**
  * A title's logo — its name as lettering — in place of [fallback], once it has
  * loaded. [fallback] stands until then, and for good when there is none, so a

android/app/src/main/java/io/narl/protonstream/ui/TitleScreen.kt

@@ -183,13 +183,7 @@ internal fun TitleScreen(
                 // the page says, and a framed thumbnail with a margin round it read
                 // as one card among the many below it.
                 Box(Modifier.sharedArt(title.key).fillMaxWidth().height(backdropHeight)) {
-                    RemoteArtwork(
-                        title.backdropUrl ?: title.posterUrl,
-                        title.displayName,
-                        Modifier.fillMaxSize(),
-                        fallback = title.thumbnailSource,
-                        labelled = false,
-                    )
+                    Backdrop(title, Modifier.fillMaxSize())
                     Box(
                         Modifier.fillMaxSize().background(
                             Brush.verticalGradient(