feat(web): rebuild web with Astro 6 + React 19 + Tailwind 4

Replace static HTML website with Astro SSG framework:
- Astro 6 + React 19 (client islands) + Tailwind CSS 4 + shadcn/ui
- i18n: zh/zh_Hant/en with URL prefix routing
- Pages: Landing, Features, Pricing, About, Privacy, Terms (3 locales)
- Responsive full-width layout with scroll reveal animations
- Cyber gradient theme with particle effects inspired by Kimi
- Features page: alternating layout with hexagram illustrations
- Legal pages: markdown rendering with side info card
- Language switcher preserves current page path
- Assets shared via symlinks to web/design/assets/ (no duplication)

Tech decisions documented in .trellis/spec/web/index.md
Task: .trellis/tasks/05-08-web-astro-react-tailwind-shadcn-ui

web/src/pages/en/about.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import AboutPage from '../../components/AboutPage.astro';
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <AboutPage locale={locale} />
+</MarketingLayout>

web/src/pages/en/features.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import FeaturesPage from '../../components/FeaturesPage.astro';
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <FeaturesPage locale={locale} />
+</MarketingLayout>

web/src/pages/en/index.astro

@@ -0,0 +1,13 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import Hero from '../../components/Hero.astro';
+import Showcase from '../../components/Showcase.astro';
+import CtaSection from '../../components/CtaSection.astro';
+
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <Hero locale={locale} />
+  <Showcase locale={locale} />
+  <CtaSection locale={locale} />
+</MarketingLayout>

web/src/pages/en/pricing.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import PricingPage from '../../components/PricingPage.astro';
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <PricingPage locale={locale} />
+</MarketingLayout>

web/src/pages/en/privacy.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="privacy_policy" />
+</MarketingLayout>

web/src/pages/en/terms.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'en' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="terms_of_service" />
+</MarketingLayout>

web/src/pages/index.astro

@@ -0,0 +1,3 @@
+---
+return Astro.redirect('/zh/');
+---

web/src/pages/zh/about.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import AboutPage from '../../components/AboutPage.astro';
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <AboutPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh/features.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import FeaturesPage from '../../components/FeaturesPage.astro';
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <FeaturesPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh/index.astro

@@ -0,0 +1,13 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import Hero from '../../components/Hero.astro';
+import Showcase from '../../components/Showcase.astro';
+import CtaSection from '../../components/CtaSection.astro';
+
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <Hero locale={locale} />
+  <Showcase locale={locale} />
+  <CtaSection locale={locale} />
+</MarketingLayout>

web/src/pages/zh/pricing.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import PricingPage from '../../components/PricingPage.astro';
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <PricingPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh/privacy.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="privacy_policy" />
+</MarketingLayout>

web/src/pages/zh/terms.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'zh' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="terms_of_service" />
+</MarketingLayout>

web/src/pages/zh_Hant/about.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import AboutPage from '../../components/AboutPage.astro';
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <AboutPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh_Hant/features.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import FeaturesPage from '../../components/FeaturesPage.astro';
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <FeaturesPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh_Hant/index.astro

@@ -0,0 +1,13 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import Hero from '../../components/Hero.astro';
+import Showcase from '../../components/Showcase.astro';
+import CtaSection from '../../components/CtaSection.astro';
+
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <Hero locale={locale} />
+  <Showcase locale={locale} />
+  <CtaSection locale={locale} />
+</MarketingLayout>

web/src/pages/zh_Hant/pricing.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import PricingPage from '../../components/PricingPage.astro';
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <PricingPage locale={locale} />
+</MarketingLayout>

web/src/pages/zh_Hant/privacy.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="privacy_policy" />
+</MarketingLayout>

web/src/pages/zh_Hant/terms.astro

@@ -0,0 +1,8 @@
+---
+import MarketingLayout from '../../layouts/Marketing.astro';
+import LegalPage from '../../components/LegalPage.astro';
+const locale = 'zh_Hant' as const;
+---
+<MarketingLayout locale={locale}>
+  <LegalPage locale={locale} docType="terms_of_service" />
+</MarketingLayout>