feat: add missing storybook stories for high-priority components

[MartianGreed]

Adds stories for components identified in the design audit as having code but no story coverage.

Stories added

• AchievementPinIcon — all 8 variants, empty states, themed with custom color
• AchievementPinIcons — 3 pins, partial pins, empty, themed, variant options
• ActivityAchievementCard — default, custom color, certified, loading, error states
• AboutDetails — short text, long text (Read More trigger), empty
• AchievementCard — single/multi-page achievements, completed/incomplete states
• ArcadeHeader — default with logo, with children (e.g. Connect button)

Context

Design audit found ~40-50% Figma coverage. These are the quick wins — components that existed in code but had no story files. More stories (marketplace cards, activity feed, nav bar, etc.) to follow in subsequent PRs.

Ref: DESIGN_AUDIT.md

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Project	Deployment	Actions	Updated (UTC)
arcade	Ready	Preview	Feb 13, 2026 1:48pm
arcade-storybook	Ready	Preview	Feb 13, 2026 1:48pm