refactor(ui): Replace ElevatedButton with FilledButton.tonal and adjust styling

Replaced `ElevatedButton` with `FilledButton.tonal` across several UI components to align with updated design principles. This change affects the main game menu, in-game menu, and the game launch screen.

- `lib/ui/main/game.dart`: Updated the game launch button.
- `lib/ui/game/in_game_menu.dart`: Updated buttons within the in-game menu.
- `lib/ui/game/action/action.dart`: Removed the `inCard` wrapper and its elevation from the action description widget for a flatter design.
- `assets/img/campfire.svg`: Deleted the unused campfire SVG asset.

Author: liplum

assets/img/campfire.svg

@@ -106,7 +106,7 @@ class _GameActionPageState extends State<GameActionPage> {
       attrs: player.attrs,
       textStyle: context.textTheme.headlineMedium,
       minHeight: 14,
-    ).padAll(12).inCard(elevation: 2);
+    ).padAll(12);
   }
 
   Widget buildJourneyProgress() {

lib/ui/game/action/action.dart

@@ -61,7 +61,7 @@ class _InGameMenuState extends State<_InGameMenu> {
   }
 
   Widget btn(String text, VoidCallback? onTap) {
-    return ElevatedButton(
+    return FilledButton.tonal(
       onPressed: onTap,
       child: text.text(
         style: TextStyle(fontSize: context.textTheme.titleLarge?.fontSize),

lib/ui/game/in_game_menu.dart

@@ -83,7 +83,7 @@ class _GamePageState extends State<GamePage> {
   }
 
   Widget buildBtn(String text, [VoidCallback? onTap]) {
-    return ElevatedButton(
+    return FilledButton.tonal(
       onPressed: onTap,
       child: text
           .autoSizeText(