refactor(renderers): satori migration — Phase 3: renderStatCard

[evirunurm]

Part of #44

Tasks

• Create scripts/renderers/StatCard.tsx
• Replace TextAttr/CardAttr interfaces and mountText/mountIcons imperative loops with flexbox column layout
• Embed SVG icon assets using satori's img or inline <svg> children
• Handle the peng/color variants via props
• Make renderStatCard async, update api/stats.ts
• Update or add tests

Depends on

• Phase 1 (refactor(renderers): migrate SVG generation to satori #44)