feat: glossy tile rendering and per-season theme colors

Introduces candy-gloss tile rendering (diagonal gradient + glass highlight
+ optional glow) via a shared paintGlossyTile() in tile_painter.dart,
applied to board filled-cells and tray/drag-overlay pieces. Adds
ThemeColors to palette.dart for UI-layer season color resolution, and
activeThemeProvider for one-call access to the active season's theme.
Regenerates the game_screen golden to reflect the new look.

lib/state/providers.dart

@@ -45,3 +45,10 @@ final seasonsProvider = FutureProvider<List<SeasonPack>>(
 final streakProvider = NotifierProvider<StreakNotifier, StreakState>(
   StreakNotifier.new,
 );
+
+/// The visual theme of whatever season is in play; fallback outside seasons
+/// (home, endless). Pure model — UI converts via ThemeColors.
+final activeThemeProvider = Provider<SeasonTheme>((ref) {
+  final flow = ref.watch(seasonFlowProvider);
+  return flow?.pack.theme ?? SeasonTheme.fallback;
+});

lib/ui/theme/palette.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import '../../game/models/season.dart';
+
 /// Season-themeable color set. Season 1 default: vivid candy tones on a
 /// deep navy board.
 class GamePalette {
@@ -24,3 +26,26 @@ class GamePalette {
   static const ghostLegal = Color(0x66FFFFFF);
   static const ghostIllegal = Color(0x55FF5252);
 }
+
+/// Resolved per-season colors for the UI layer. Built from a SeasonTheme;
+/// falls back to the GamePalette constants.
+class ThemeColors {
+  ThemeColors(SeasonTheme theme)
+      : gradient = [for (final c in theme.backgroundGradient) Color(c)],
+        accent = Color(theme.accentColor),
+        particleType = theme.particleType,
+        board = theme.boardTint != null
+            ? Color(theme.boardTint!)
+            : GamePalette.boardBackground,
+        tiles = theme.tilePalette != null
+            ? [for (final c in theme.tilePalette!) Color(c)]
+            : GamePalette.tileColors;
+
+  final List<Color> gradient;
+  final Color accent;
+  final String particleType;
+  final Color board;
+  final List<Color> tiles;
+
+  Color tile(int colorId) => tiles[colorId % tiles.length];
+}

lib/ui/widgets/board_painter.dart

@@ -6,6 +6,7 @@ import '../../game/models/piece.dart';
 import '../theme/palette.dart';
 import 'board_geometry.dart';
 import 'piece_painter.dart';
+import 'tile_painter.dart';
 
 /// Drag ghost preview: a piece hovering at a snapped anchor.
 class GhostSpec {
@@ -55,27 +56,20 @@ class BoardPainter extends CustomPainter {
       for (var x = 0; x < GridState.size; x++) {
         final rect = geo.cellRect(x, y).deflate(inset);
         final cell = grid.cellAt(x, y);
-        final paint = Paint()
-          ..color = switch (cell.type) {
-            CellType.empty => GamePalette.emptyCell,
-            CellType.filled => GamePalette.tile(cell.colorId),
-            CellType.gem => GamePalette.emptyCell,
-          };
-        canvas.drawRRect(RRect.fromRectAndRadius(rect, radius), paint);
-
-        if (cell.type == CellType.gem) {
-          _paintGem(canvas, rect);
-        } else if (cell.type == CellType.filled) {
-          final highlight = Paint()
-            ..color = Colors.white.withValues(alpha: 0.15);
+        switch (cell.type) {
+          case CellType.empty:
             canvas.drawRRect(
-            RRect.fromRectAndRadius(
-              Rect.fromLTWH(
-                  rect.left, rect.top, rect.width, rect.height * 0.32),
-              radius,
-            ),
-            highlight,
+              RRect.fromRectAndRadius(rect, radius),
+              Paint()..color = GamePalette.emptyCell,
             );
+          case CellType.filled:
+            paintGlossyTile(canvas, rect, GamePalette.tile(cell.colorId));
+          case CellType.gem:
+            canvas.drawRRect(
+              RRect.fromRectAndRadius(rect, radius),
+              Paint()..color = GamePalette.emptyCell,
+            );
+            _paintGem(canvas, rect);
         }
       }
     }
@@ -111,6 +105,10 @@ class BoardPainter extends CustomPainter {
   }
 
   void _paintGem(Canvas canvas, Rect rect) {
+    final glowPaint = Paint()
+      ..color = GamePalette.gem.withValues(alpha: 0.45)
+      ..maskFilter = MaskFilter.blur(BlurStyle.normal, rect.width * 0.25);
+    canvas.drawCircle(rect.center, rect.width * 0.32, glowPaint);
     final center = rect.center;
     final r = rect.width * 0.32;
     final path = Path()

lib/ui/widgets/piece_painter.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 
 import '../../game/models/piece.dart';
 import '../theme/palette.dart';
+import 'tile_painter.dart';
 
 /// Draws a piece as rounded tiles at a given cell size; reused by the tray,
 /// the drag overlay, and ghost previews.
@@ -12,8 +13,6 @@ void paintPiece(
   Offset origin = Offset.zero,
   Color? overrideColor,
 }) {
-  final paint = Paint()
-    ..color = overrideColor ?? GamePalette.tile(piece.colorId);
   final inset = cellSize * 0.05;
   final radius = Radius.circular(cellSize * 0.18);
   for (final (dx, dy) in piece.offsets) {
@@ -23,17 +22,13 @@ void paintPiece(
       cellSize - inset * 2,
       cellSize - inset * 2,
     );
-    canvas.drawRRect(RRect.fromRectAndRadius(rect, radius), paint);
-    if (overrideColor == null) {
-      // Subtle top highlight for depth.
-      final highlight = Paint()..color = Colors.white.withValues(alpha: 0.18);
+    if (overrideColor != null) {
       canvas.drawRRect(
-        RRect.fromRectAndRadius(
-          Rect.fromLTWH(rect.left, rect.top, rect.width, rect.height * 0.32),
-          radius,
-        ),
-        highlight,
+        RRect.fromRectAndRadius(rect, radius),
+        Paint()..color = overrideColor,
       );
+    } else {
+      paintGlossyTile(canvas, rect, GamePalette.tile(piece.colorId));
     }
   }
 }

lib/ui/widgets/tile_painter.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+
+Color lighten(Color c, double amount) => Color.lerp(c, Colors.white, amount)!;
+Color darken(Color c, double amount) => Color.lerp(c, Colors.black, amount)!;
+
+/// Candy-gloss tile: diagonal gradient body, glass top highlight, optional
+/// colored glow (used for gems and clear flashes). Shared by the board,
+/// tray, and drag overlay so every tile in the game matches.
+void paintGlossyTile(
+  Canvas canvas,
+  Rect rect,
+  Color color, {
+  double radiusFactor = 0.18,
+  double glow = 0,
+}) {
+  final radius = Radius.circular(rect.width * radiusFactor);
+  final rrect = RRect.fromRectAndRadius(rect, radius);
+
+  if (glow > 0) {
+    final glowPaint = Paint()
+      ..color = color.withValues(alpha: 0.55 * glow)
+      ..maskFilter =
+          MaskFilter.blur(BlurStyle.normal, rect.width * 0.28 * glow);
+    canvas.drawRRect(rrect.inflate(rect.width * 0.05), glowPaint);
+  }
+
+  final body = Paint()
+    ..shader = LinearGradient(
+      begin: Alignment.topLeft,
+      end: Alignment.bottomRight,
+      colors: [lighten(color, 0.28), color, darken(color, 0.22)],
+      stops: const [0.0, 0.45, 1.0],
+    ).createShader(rect);
+  canvas.drawRRect(rrect, body);
+
+  final highlight = Paint()..color = Colors.white.withValues(alpha: 0.30);
+  final hl = Rect.fromLTWH(
+    rect.left + rect.width * 0.10,
+    rect.top + rect.height * 0.07,
+    rect.width * 0.80,
+    rect.height * 0.30,
+  );
+  canvas.drawRRect(
+    RRect.fromRectAndRadius(hl, Radius.circular(rect.width * 0.12)),
+    highlight,
+  );
+}