feat(snake): wrap snake through walls instead of crashing

[clovisphere]

Summary

• nextHead now wraps using modulo instead of returning null on wall contact
• Removed the wall-crash check from the game loop in main.js
• Updated the "How to play" overlay to reflect the new behaviour
• Updated README rules section accordingly

Test plan

• 47/47 tests pass (bun test)
• Snake wraps left→right, right→left, top→bottom, bottom→top
• Self-collision and timer expiry still cost a life
• "How to play" overlay shows the correct wall behaviour

Summary by CodeRabbit

Release Notes

• New Features

  • Wall wrapping: Hitting a wall now wraps the snake to the opposite side with no penalty. Colliding with your tail or letting the clock expire still costs a life.
  • Added smooth wrap-around transition animation.

• Documentation

  • Updated in-game rules and help text to clarify the new wall-wrapping mechanic.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c774267a-e8c0-45fe-baee-daf8758dcc8d

📥 Commits

Reviewing files that changed from the base of the PR and between 73cd5a2 and a2c8db9.

📒 Files selected for processing (6)

• README.md
• public/css/style.css
• public/js/main.js
• public/js/snake.js
• public/js/ui.js
• tests/snake.test.js

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📝 Walkthrough

Walkthrough

Wall-collision death is replaced with modulo-based wrap-around in nextHead. The game loop tracks a wrapGhost state object populated in step() when a boundary is crossed; renderGrid uses it to animate a ghost head sliding off one edge while the real head enters from the opposite side. Tests, README, and in-game help text are updated to match.

Changes

Wall Wrap Feature

Layer / File(s)	Summary
nextHead wrap logic and step() wrapGhost state public/js/snake.js, tests/snake.test.js, public/js/main.js	nextHead uses modulo to always return a valid in-bounds position instead of null; step() detects boundary crossings and sets G.wrapGhost with entry/exit coordinates; startGame() initializes wrapGhost: null; tests assert wrapped coordinates instead of null for each boundary direction.
Wrap ghost animation rendering public/js/ui.js, public/js/main.js, public/css/style.css	render() clears G.wrapGhost each frame; renderGrid builds the head element separately, attaches optional wrapFrom per segment, spawns a temporary exit-ghost element that animates off the edge, and applies notrans + translated transform to wrap-entering segments for a snap-in effect; .ent rule repositioned in stylesheet.
Copy updates README.md, public/js/ui.js	README splits the life-loss bullet into wall-wrap (no penalty) and tail/clock (costs a life); in-game helpHTML updated to match.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐍 The wall was once a deadly foe,
now I zoom through, high and low.
Modulo math, a gentle trick—
ghost slides out, then snaps in quick.
No life lost, just round I go! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main feature change: implementing wall-wrapping instead of crashing for the snake game.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/wall-wrapping

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