tweak(ui): shimmering titles and animated counts

[kitlangton]

CleanShot.2026-02-27.at.21.22.44.mp4

Summary

• Refactored text shimmer to use background-clip: text gradient sweep instead of per-character color cycling
• Extracted ToolStatusTitle component for animated active/done label transitions (e.g. "Exploring" → "Explored")
• Added AnimatedNumber odometer digit roller, AnimatedCountLabel with i18n-aware plural suffix animation, and AnimatedCountList for the context tool group summary
• Fixed plural suffix spacing bug caused by ch unit approximation — now uses grid-template-columns: 0fr → 1fr for pixel-perfect width
• Added prefers-reduced-motion support across all new CSS files
• Cleaned up broken storybook stories (code, diff, diff-ssr) and removed unused Code/Diff providers from preview
• Bumped storybook from 10.2.10 → 10.2.13
• Added dev:storybook script to root package.json
• Added interactive storybook story with simulation, 8-locale i18n picker, and reduced-motion toggle

Test plan

• Verify shimmer sweep animation on "Exploring" / tool titles in the session view
• Verify "Explored 2 reads, 5 searches" counts animate in correctly with no spacing gaps
• Toggle between languages in the app to confirm i18n strings render properly
• Check prefers-reduced-motion disables all animations (OS setting or storybook toggle)
• Run bun run dev:storybook and verify the AnimatedCountList story loads and works