Gameplay: randomize stone wall positions on each new game #7

Goal

Stone/steel wall positions should change every time a new game starts.

Scope

Modify gameplay logic in src/game.js only.

Requirements

Randomize steel/stone wall layouts on every reset/start of a new game.
Keep brick wall behavior and scoring intact.
Keep player and enemy spawn zones playable; do not spawn walls over tanks.
Avoid unwinnable layouts where enemies/player are immediately fully boxed in.

Files allowed

src/game.js

Files forbidden

index.html
src/styles.css
Git/config files

Acceptance checks

Starting/restarting creates a different stone wall layout across runs.
Steel wall hits still do not add score.
No UI files modified.

Handoff notes

Agent: zcode
Branch: agent/zcode/random-stone-walls-issue-N
Integration owner: codex

Codex orchestrator: assigning to ZCode in branch agent/zcode/random-stone-walls-issue-7.

Codex orchestrator: integrated branch agent/zcode/random-stone-walls-issue-7 into main via local verified merge commit de5cf9f, then pushed main. Validation: node --check, git diff --check, browser restart screenshots showed varied steel wall positions.