feat(analytics): add range selector and shadcn-style area chart

- 7d / 30d / 6m / 1y toggle that swaps granularity (daily, weekly,
  monthly buckets) and re-derives the trend chart from the same
  attempts query
- New smooth area chart with dedicated Y axis, sparse X labels, and
  hover tooltips on each bucket
- Pink fill gradient + soft accent dot in the footer to match the
  shadcn area-chart aesthetic while keeping our pink/cyan theme
- Footer summarises totals and completion rate for the chosen window

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: 2 people