fix(game): restore effect-seven multiball

Arm effect 7 after the wheel-reset target, select it on the next effect line,
and spawn a second visible live ball when record 149 is consumed. Advance the
second ball through recovered line, circle, ball-ball, magnetic, and scoring
collisions independently.

During multiball, draining one ball leaves the other active without consuming a
remaining player ball. Include secondary state in deterministic traces and
finite-state validation.

Test Plan:
- `cargo test --all-targets` -- 52 passed
- `cargo clippy --all-targets -- -D warnings` -- passed
- production build plus Windows GNU and macOS checks -- passed
- effect-seven spawn, movement, and single-drain lifecycle test -- passed
- `git diff --cached --check` -- passed

tdkpin-rs/src/app.rs

@@ -493,6 +493,14 @@ impl App {
                 WHITE,
             );
         }
+        if let Some(ball) = game.secondary_ball {
+            draw_texture(
+                &self.assets.ball,
+                ball.position.x - 8.0,
+                ball.position.y - 8.0,
+                WHITE,
+            );
+        }
         if let Some(source) = game.claw.sprite_source() {
             draw_texture_ex(
                 &self.assets.robot,