fix(input): require plus to start players

Remove the Enter shortcut so the start flow matches the original plus-key handler. Use the recovered player-add sound resource for both the first and subsequent players.

Test Plan:
- cargo fmt --check
- cargo test
- cargo clippy --all-targets --all-features -- -D warnings
- git diff --cached --check

tdkpin-rs/README.md

@@ -51,7 +51,7 @@ and `claw-18`; `--seed N` fixes random choices for later seeded scenarios.
 
 | Action | Original key | Additional modern key |
 | --- | --- | --- |
-| Start game / add up to 4 players | `+` | `=` or Enter starts one player |
+| Start game / add up to 4 players | `+` | `=` uses the same main-keyboard key |
 | Charge launcher | Hold Down arrow, release to launch | - |
 | Left flipper | Left Ctrl | `A` or Left arrow |
 | Right flipper | Keypad Enter | Right Ctrl, `D`, or Right arrow |

tdkpin-rs/src/app.rs

@@ -150,13 +150,10 @@ impl App {
     }
 
     fn update_attract(&mut self) {
-        if is_key_pressed(KeyCode::KpAdd)
-            || is_key_pressed(KeyCode::Equal)
-            || is_key_pressed(KeyCode::Enter)
-        {
+        if is_key_pressed(KeyCode::KpAdd) || is_key_pressed(KeyCode::Equal) {
             self.game = Some(Game::new(1));
             self.screen = Screen::Playing;
-            self.assets.play(2008, self.saved.settings.sounds);
+            self.assets.play(2001, self.saved.settings.sounds);
         }
     }
 
@@ -167,7 +164,7 @@ impl App {
                 .as_mut()
                 .is_some_and(Game::add_player_before_launch)
         {
-            self.assets.play(2012, self.saved.settings.sounds);
+            self.assets.play(2001, self.saved.settings.sounds);
         }
         let left_flipper = is_key_down(KeyCode::LeftControl)
             || is_key_down(KeyCode::A)