Fix Safari SVG display for halftone pattern elements

Replace SVG files that use halftone patterns with original versions
from backup to fix Safari rendering issues.

Files replaced:
- sunburst.svg
- illust-sub.svg
- bg.svg, bg-dark.svg
- fire.svg, mimi.svg, ivan.svg, train.svg, game.svg
- footer/illust-pattern.svg

Fixes #253

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: taea