feat: Sharp style, Tailwind+shadcn, dark navbar, nav restructure, Go/monorepo guidelines

Styling:
- Tailwind CSS v4 (preflight:false) integrated via PostCSS plugin
- shadcn/ui New York style with --radius:0 (sharp corners everywhere)
- Zero border-radius on ALL elements: buttons, code blocks, cards, admonitions, badges
- Navbar FORCE dark (#0a0a0a) in both light/dark modes via !important
- ThemeSynchronizer: bridges Docusaurus data-theme → shadcn .dark class
- Active sidebar item gets left border accent instead of rounded bg

React UI components (src/components/ui/index.tsx):
- Badge (6 variants: wip, stable, planned, success, warning, outline)
- Card + CardHeader + CardTitle + CardContent
- Callout (note/info/success/warning/danger) - sharp, left-border style
- PropertiesTable - monospace typed API reference tables
- StatusIndicator - operational/degraded/outage/maintenance

Navigation restructure:
- Introduction → Platform → Products → Engineering → Runbooks
- Old 'applications/' removed, moved to products/stock-market-pro/
- New Platform section: infrastructure overview + CI/CD pipeline docs
- New Engineering section: monorepo structure, Go stack, conventions
- New Runbooks section: incident severity, common procedures

Implementation guidelines (engineering/guidelines.md):
- Monorepo layout with go.work workspace
- Go as primary language (why + standard library table)
- Python as sidecar for data/ML workloads
- Code conventions: gofmt, error wrapping, logging, testing
- Git conventions: branch naming, conventional commits
- Makefile targets per app
- How to add a new application (step-by-step)

package.json

@@ -18,20 +18,28 @@
     "@docusaurus/core": "3.10.2",
     "@docusaurus/faster": "3.10.2",
     "@docusaurus/preset-classic": "3.10.2",
+    "@docusaurus/theme-common": "^3.10.2",
     "@docusaurus/theme-mermaid": "^3.10.2",
     "@mdx-js/react": "^3.0.0",
-    "clsx": "^2.0.0",
+    "@radix-ui/react-slot": "^1.3.0",
+    "@radix-ui/react-tooltip": "^1.2.12",
+    "clsx": "^2.1.1",
     "docusaurus-plugin-drawio": "^0.4.0",
     "prism-react-renderer": "^2.3.0",
     "raw-loader": "^4.0.2",
     "react": "^19.0.0",
-    "react-dom": "^19.0.0"
+    "react-dom": "^19.0.0",
+    "server-only": "^0.0.1",
+    "tailwind-merge": "^3.6.0"
   },
   "devDependencies": {
     "@docusaurus/module-type-aliases": "3.10.2",
     "@docusaurus/tsconfig": "3.10.2",
     "@docusaurus/types": "3.10.2",
     "@types/react": "^19.0.0",
+    "autoprefixer": "^10.5.3",
+    "postcss": "^8.5.19",
+    "tailwindcss": "^4.3.2",
     "typescript": "~6.0.2"
   },
   "browserslist": {