feat(landing): introduce Orchid on the 0.email home page

[MrgSub]

Summary

Replaces the legacy Zero marketing landing on / and /home with a single-screen "0.email is now Orchid" announcement that hands visitors off to orchid.ai, while preserving a clear sign-in path for existing users and a link to the OSS repo.

Old HomeContent.tsx (multi-section marketing page with feature tabs, AI summary cards, search demo, etc.) is fully replaced — net +304 / −1288 LOC.

What it looks like

A cinematic dark hero, designed in Orchid's visual language but bridged to 0.email's mental model:

1. Backdrop — masked Orchid hero video (top-right), warm gold halo, deep violet pool, mountain texture at 4% opacity, radial vignette over the copy.
2. Eyebrow chip — "A NEW CHAPTER" with a pulsing gold dot.
3. Headline reveal (serif, ~clamp 44–96px):
   • Line 1 fades in: 0.email is now
   • A gradient gold strikethrough draws across "0.email" left→right.
   • Line 2 reveals: Orchid. (white → cream → gold gradient text) with the orchid logomark scaling/rotating in beside it.
4. Body copy — "What started as the fastest open-source inbox grew into something bigger. Orchid is the executive assistant that doesn't sleep…"
5. CTAs, in priority order:
   • Meet Orchid → (white pill) → https://orchid.ai
   • Sign in to Zero (ghost pill) → https://app.0.email
   • GitHub (ghost pill, with live ★ count) → https://github.com/Mail-0/Zero
6. Fineprint — Read the announcement (→ orchid.ai/blog/the-end-of-inbox-zero), Privacy, Terms, ©.

Implementation notes

• Inline <OrchidMark /> SVG component (5-petal mark) using currentColor, stroke-linejoin="round", and shape-rendering="geometricPrecision" so it stays crisp at any size and renders white on the dark backdrop.
• All animation via motion/react with prefers-reduced-motion respected (orchid video pauses, headline reveals still work but no blur/translate).
• GitHub star count cached for 5 min via TanStack Query (re-using the existing query pattern from navigation.tsx); pill is hidden until count > 0 to avoid flashing a "0".
• Assets imported from apps/site/public/:
  • orchid-hero.webm / .mp4 / poster
  • orchid-mask.svg
  • orchid-mountain.jpeg
• No route changes — app/page.tsx and app/home/page.tsx already render <HomeContent />.

What this does not change

• Sign-in / OAuth flow itself (handled by app.0.email).
• /pricing, /about, /privacy, /terms, /contributors — still live.
• The old Navigation + Footer components are no longer rendered on /, but are not deleted (still used by other pages).

Test plan

• / and /home render the new landing on desktop + mobile
• All three CTAs open correct destinations (Orchid / app.0.email / GitHub)
• Headline animation sequence plays in order; nothing pops
• prefers-reduced-motion: video paused, no aggressive entrance animations
• GitHub star count loads (or pill is hidden if GH is rate-limited)
• Lighthouse / perf: the hero video preload doesn't blow up LCP