feat(landing): alerting homepage section + redesigned /features/alerting page

[Makisuo]

What changed

New homepage section (Alerting.astro) — centered stage with the firing-incident artifact (live/LiveAlertFeed.astro, SSR-only, reduced-motion-gated pulse), chips for every notification destination (Slack, Discord, PagerDuty, email, webhook, Hazel), and a 3-card feature strip. Localized in en/ja/ko (messages + regenerated paraglide output).

Redesigned /features/alerting — rebuilt from hero → single card → text grids to the same quality bar as the Kubernetes feature page:

• Rule evaluation: a live-frame mock with the rule expression and an SVG evaluation chart — signal crossing the dashed 2% threshold, breach segment in severity-red, "for 5m" persistence bracket, fired marker — connected by an arrow to the resulting incident card. Footer states the preview result plainly.
• Group fan-out: three region rows (one firing with its delivery log, two quiet), one incident per group.
• Destinations grid: brand icons + a mono delivery sample line per destination.
• Incident lifecycle: Triggered → Notified → Renotified → Auto-resolved timeline with severity-colored dots and tabular timestamps.

FAQ/detail-grid/SEO content unchanged so AI-extraction copy stays intact.

Notes for review

• All mock data is consistent across artifacts (same 4.7% / eu-west-1 incident everywhere).
• Feature-page copy is hardcoded English, matching the other feature pages; only the homepage section is localized.
• Verified in the browser at desktop and mobile widths: no horizontal overflow, islands hydrate, no console errors beyond the known Clerk dev-key noise.

🤖 Generated with Claude Code

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