fix(ui): keep hero titles and clear logos legible in light theme

On the light theme, the detail hero's fallback title was hard-coded
white over a scrim that washes artwork toward the near-white background,
and white-on-transparent clear logos vanished into the same wash on the
detail, home, and TV spotlight heroes.

The title fallback now defaults to the theme foreground with a
background-side halo, matching what the TV hero already did. Clear logos
run through the channel-logo tone remap: light-toned marks recolor
toward the theme foreground on light backdrops (network and downloaded
artwork alike), colored marks keep their pixels, and dark themes render
the original artwork. The backdrop-luminance gate is shared with the
Live TV guide as logoToneTargetFor.

test/utils/tone_mapped_logo_image_test.dart

@@ -111,4 +111,19 @@ void main() {
     plain.dispose();
     expect(PaintingBinding.instance.imageCache.currentSize, 2);
   });
+
+  test('logoToneTargetFor engages only over light backdrops', () {
+    const foreground = Color(0xFF111111);
+    // Light theme surfaces and backgrounds.
+    expect(logoToneTargetFor(surface: const Color(0xFFFFFFFF), foreground: foreground), foreground);
+    expect(logoToneTargetFor(surface: const Color(0xFFF7F7F8), foreground: foreground), foreground);
+    // Dark theme surfaces and the light theme's inverted (dark) focus card.
+    expect(logoToneTargetFor(surface: const Color(0xFF15171C), foreground: foreground), isNull);
+    expect(logoToneTargetFor(surface: const Color(0xFF111111), foreground: foreground), isNull);
+    // The dark theme's inverted focus card is light and re-engages the remap.
+    expect(
+      logoToneTargetFor(surface: const Color(0xFFEDEDED), foreground: const Color(0xFF0E0F12)),
+      const Color(0xFF0E0F12),
+    );
+  });
 }