feat: add refractor tier-specific card art rendering
Implement tier-aware visual styling for card PNG rendering (T0-T4).
Each refractor tier gets distinct borders, header backgrounds, column
header gradients, diamond tier indicators, and decorative effects.
- New tier_style.html template: per-tier CSS overrides (borders, headers,
gradients, inset glow, diamond positioning, corner accents)
- Diamond indicator: 2x2 CSS grid rotated 45deg at header/result boundary,
progressive fill (1B→2B→3B→Home) with tier-specific colors
- T4 Superfractor: bold gold borders, dual gold-teal glow, corner accents,
purple diamond with glow pulse animation
- resolve_refractor_tier() helper: pure-math tier lookup from variant hash
- T3/T4 animations defined but paused for static PNG capture (APNG follow-up)
Relates-to: initiative #19
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
b32e19a4ac