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/tsconfig.json

@@ -0,0 +1,16 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "include": [
+    ".astro/types.d.ts",
+    "**/*"
+  ],
+  "exclude": [
+    "dist"
+  ],
+  "compilerOptions": {
+    "jsx": "react-jsx",
+    "jsxImportSource": "react",
+    "resolveJsonModule": true,
+    "esModuleInterop": true
+  }
+}