fix(android): default to classic theme to fix AMOLED card-back invisibility

Dark theme back.svg uses #151515 (near-black) as the card back background,
which AMOLED screens render as fully-off pixels, leaving only the tiny
#a54242 red badge visible — user sees solid red squares instead of card backs.

Fix: change fresh-install default theme from "dark" to "classic" (white
background with navy diamond pattern, clearly visible on all display types).
Also remove the stale "classic" -> "dark" sanitize migration, correct wrong
asset paths in load_card_images (classic/ subdirectory was missing), and
update tests that hardcoded the old TABLEAU_FAN_FRAC=0.25 constant.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -6,6 +6,20 @@ project follows [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
+## [0.31.0] — 2026-05-16
+
+### Fixed
+
+- **Face-down cards rendered as solid red squares on AMOLED phones** (Bug 1).
+  The dark theme's card back (`back.svg`) uses a near-black background
+  (`#151515`) which AMOLED screens render as fully-off pixels, leaving only a
+  tiny `#a54242` red badge visible — exactly what was reported. Fixed by
+  changing the fresh-install default theme from "dark" to "classic" (white
+  background with navy diamond pattern, clearly readable on all display types).
+  Also corrected stale asset paths in `load_card_images` (`cards/backs/back_N`
+  → `cards/backs/classic/back_N`, `cards/faces/XY` → `cards/faces/classic/XY`)
+  so the PNG fallback loads correctly when the embedded theme hasn't arrived yet.
+
 ## [0.30.0] — 2026-05-16
 
 ### Changed

solitaire_data/src/settings.rs

@@ -275,7 +275,7 @@ fn default_music_volume() -> f32 {
 }
 
 fn default_theme_id() -> String {
-    "dark".to_string()
+    "classic".to_string()
 }
 
 /// Default tooltip-hover dwell delay in seconds. Mirrors
@@ -402,11 +402,10 @@ impl Settings {
     /// their respective ranges after deserialization or hand-editing of
     /// `settings.json`.
     pub fn sanitized(self) -> Self {
-        // Migrate stale theme IDs: "default" was removed when the theme was
-        // renamed to "dark"; "classic" was briefly the default before "dark"
-        // was restored as the shipped default.
+        // Migrate stale theme IDs: "default" was the original name before it
+        // was renamed to "dark".
         let selected_theme_id = match self.selected_theme_id.as_str() {
-            "default" | "classic" => "dark".to_string(),
+            "default" => "dark".to_string(),
             _ => self.selected_theme_id,
         };
         Self {

solitaire_engine/src/card_plugin.rs

@@ -484,13 +484,13 @@ fn load_card_images(asset_server: Option<Res<AssetServer>>, mut commands: Comman
     let faces: [[Handle<Image>; 13]; 4] = std::array::from_fn(|suit| {
         std::array::from_fn(|rank| {
             asset_server.load(format!(
-                "cards/faces/{}{}.png",
+                "cards/faces/classic/{}{}.png",
                 RANK_STRS[rank], SUIT_CHARS[suit]
             ))
         })
     });
     let backs = std::array::from_fn(|i| {
-        asset_server.load(format!("cards/backs/back_{i}.png"))
+        asset_server.load(format!("cards/backs/classic/back_{i}.png"))
     });
     commands.insert_resource(CardImageSet {
         faces,

solitaire_engine/src/input_plugin.rs

@@ -1785,9 +1785,8 @@ mod tests {
         let layout = compute_layout(Vec2::new(1280.0, 800.0), 0.0, 0.0, true);
         // Tableau 6 has 7 cards.
         let (_, size) = pile_drop_rect(&PileType::Tableau(6), &layout, &game);
-        // Expected: card_height + 6 * fan. fan = 0.25 * card_height, so
-        // size.y = card_height * (1 + 6 * 0.25) = card_height * 2.5.
-        let expected = layout.card_size.y * 2.5;
+        // Expected: card_height + 6 fan steps.
+        let expected = layout.card_size.y * (1.0 + 6.0 * layout.tableau_fan_frac);
         assert!(
             (size.y - expected).abs() < 1e-3,
             "expected {expected}, got {}",