feat: setup React + Vite + TypeScript frontend with Tailwind CSS

Initialize frontend infrastructure for Sprint 3 Landing Page:

Infrastructure Setup:
- Create React + Vite + TypeScript project in frontend/ directory
- Install Tailwind CSS, PostCSS, Autoprefixer dependencies
- Generate tailwind.config.js with content paths
- Generate postcss.config.js with plugins configuration
- Add Tailwind directives (@tailwind base/components/utilities) to src/index.css
- Update root .gitignore to exclude frontend/node_modules and build artifacts

Documentation Updates:
- Add CHANGELOG.md entry for Sprint 3 Landing Page development start
- Update README.md with frontend development instructions
- Add Node.js and npm prerequisites
- Document npm commands: install, dev, build, preview

Project Structure:
├── frontend/
│   ├── src/
│   │   ├── App.tsx
│   │   ├── main.tsx
│   │   ├── index.css (with Tailwind)
│   │   └── assets/
│   ├── index.html
│   ├── package.json
│   ├── tailwind.config.js
│   ├── postcss.config.js
│   └── vite.config.ts

Safety First:
- Verified directory doesn't exist before creation
- Checked all configuration files are valid
- Excluded node_modules from git
- No project code modified, only new frontend directory added

Refs: docs/frontend_landing_plan.md
Next: Start developing landing page components

README.md

@@ -45,7 +45,8 @@ Il progetto segue una metodologia **Spec-Driven** e **TDD** (Test-Driven Develop
 - **Python** 3.12 o superiore
 - **Bash** 4.0+
 - **curl** (GNU coreutils)
-- **Node.js** 18+ (per i MCP servers)
+- **Node.js** 18+ (per i MCP servers e frontend)
+- **npm** 9+ (per il frontend)
 
 ### Clone e setup
 
@@ -111,6 +112,35 @@ pytest tests/test_logwhisperer.py -v --tb=short
 ./scripts/logwhisperer.sh --config /etc/logwhisperer/config.env
 ```
 
+### Sviluppo Frontend (Landing Page)
+
+Il progetto include una landing page moderna costruita con React, Vite e Tailwind CSS.
+
+```bash
+# Entra nella directory frontend
+cd frontend
+
+# Installa le dipendenze (prima volta)
+npm install
+
+# Avvia il server di sviluppo
+npm run dev
+
+# Build per produzione
+npm run build
+
+# Preview della build
+npm run preview
+```
+
+**Stack Frontend:**
+- **React 18** + **TypeScript** - UI library con type safety
+- **Vite** - Build tool veloce con HMR
+- **Tailwind CSS** - Utility-first CSS framework
+- **PostCSS** + **Autoprefixer** - Processing CSS
+
+La landing page sarà disponibile su `http://localhost:5173` durante lo sviluppo.
+
 
 ## 🤖 Agenti AI (OpenCode.ai)