feat(site): refine landing power demos

[wibus-wee]

Summary

• replace the landing usage placeholder with the real stats and usage visualization components backed by deterministic, intentionally irregular demo data
• keep the usage preview manually scrollable with natural document scroll chaining, while page scroll drives the display-only PR preview after half of the frame enters
• rotate usage ranges every 1.5 seconds only while visible, add detailed day breakdowns and complete chart colors, and preserve circular 7-day matrix dots in the narrow landing frame

Context

The usage data is deliberately uneven across days and hours instead of following a clean weekday or weekend pattern. The 7-day view keeps 02:00 through 06:00 quiet while allowing large differences between daily totals. The usage panel remains directly scrollable; reaching its top or bottom hands the wheel gesture back to the page.

Validation

• pnpm --dir site-docs exec tsc --noEmit
• pnpm exec oxlint site-docs/components/landing-power-demo-data.ts site-docs/components/landing-power-demos.tsx site-docs/components/landing-power-i18n.ts site-docs/components/landing-power-section.tsx site-docs/types/lody-app-components.d.ts
• pnpm --dir site-docs exec vite build
• git diff --check
• Chromium interaction checks for usage scroll chaining, PR progress, 7-day quiet hours, daily variance, chart palette, and dot geometry