Add snake terminal example

[joshka]

Summary

• add a multi-file terminal Snake example using Bevy resources/messages/systems and Ratatui rendering
• include board sizing, HUD/controls, pause and game-over overlays, buffered input, crash grace, level-based speed, high score, restart, and smooth partial-block head/tail movement
• document the example structure and fix nearby Rustdoc links that pointed at the old input translation path

Validation

• cargo fmt --all --check
• cargo check --example snake
• cargo test --example snake
• cargo check --workspace --all-targets
• cargo doc --example snake --no-deps
• markdownlint-cli2 --config ~/.markdownlint-cli2.yaml README.md examples/snake/README.md

Notes

Manual terminal smoke testing is still worth doing during review for controls, resize behavior, and animation feel.

[joshka]

[gold-silver-copper]

love this