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

original/MECHANICS_PROGRESS.md

@@ -188,6 +188,12 @@ per-player effect word, and activated type-4 record 149. `1000:c4e1` maps effect
 the accumulated bonus to score. Entering record 149 also awards its static 500,
 clears the selection, and disables the record until line 84 is hit again.
 
+After record 148 sets `DAT_1028_399a`, the next flagged line-84 selection uses
+effect 7 instead of random 1-6. The effect-7 branch in `1000:c4e1` schedules the
+timer's second-ball path and raises the active-ball count to two. The Rust port
+now keeps and renders a second live ball, applies recovered physical collisions
+and scores to it, and removes only the drained ball while multiball is active.
+
 The score-addition path at `1000:bc36` indexes the initialized 32-bit threshold
 table at DGROUP `0x825` using media state 1-4. The exact thresholds are 140,000,
 650,000, 1,300,000, and 4,000,000. Crossing each threshold increments the media