compute and persist the artist name busy flag with the artwork seed

- ArtworkSeedStore now carries the flag; artwork_seeds gains a nullable nameBusy column
  (DB v12, migration 11->12) so it survives cold starts with no decode
- resolve() computes the flag from the same bitmap it extracts the colour seed from, so
  there is no second decode, and persists it alongside the seed
- overlaidNameBusy reuses the seed job and reads the cached flag synchronously, so the
  scrim is known before the art shows; drop the fade
- bottomBandBusy now uses perceptual (gamma-space) luma, edge density and a bright
  fraction, which catches busy art on dark backgrounds (issue #40) that mean/variance missed

app/src/test/kotlin/com/subtracks/ui/theme/ArtworkNameBandTest.kt

@@ -26,6 +26,11 @@ class ArtworkNameBandTest {
         assertFalse(ArtworkSeedCache.bottomBandBusy(bitmap { _, _ -> Color.rgb(24, 20, 34) }))
     }
 
+    @Test
+    fun smoothDarkGradientNeedsNoScrim() {
+        assertFalse(ArtworkSeedCache.bottomBandBusy(bitmap { x, _ -> Color.rgb(x * 2, x * 2, x * 2) }))
+    }
+
     @Test
     fun brightBandNeedsAScrim() {
         assertTrue(ArtworkSeedCache.bottomBandBusy(bitmap { _, _ -> Color.rgb(235, 230, 220) }))
@@ -35,4 +40,13 @@ class ArtworkNameBandTest {
     fun noisyBandNeedsAScrim() {
         assertTrue(ArtworkSeedCache.bottomBandBusy(bitmap { x, y -> if ((x + y) % 2 == 0) Color.WHITE else Color.BLACK }))
     }
+
+    @Test
+    fun darkBandWithBrightStrokesNeedsAScrim() {
+        assertTrue(
+            ArtworkSeedCache.bottomBandBusy(
+                bitmap { x, y -> if (x % 9 == 0 || y % 9 == 0) Color.rgb(210, 40, 40) else Color.BLACK },
+            ),
+        )
+    }
 }