docs(design-system): add design system documentation and AI agent instructions

- Add docs/design-system.md with color tokens, typography, spacing, icons, responsive/PWA rules and component reuse guidelines
- Add CLAUDE.md with permanent instructions for Claude Code
- Add .github/instructions/design-system.instruction.md for GitHub Copilot
- Update .github/copilot-instructions.md to reference the design system
- Update Front-End/tailwind.config.js with color tokens (primary, secondary, tertiary, neutral) and font families (Manrope/Inter)
- Update Front-End/src/app/layout.js to load Manrope and Inter via next/font/google

Front-End/tailwind.config.js

@@ -4,7 +4,25 @@ module.exports = {
     './src/**/*.{js,jsx,ts,tsx}', // Ajustez ce chemin selon la structure de votre projet
   ],
   theme: {
-    extend: {},
+    extend: {
+      colors: {
+        primary: '#059669',
+        secondary: '#064E3B',
+        tertiary: '#10B981',
+        neutral: '#F8FAFC',
+      },
+      fontFamily: {
+        headline: ['var(--font-manrope)', 'Manrope', 'sans-serif'],
+        body: ['var(--font-inter)', 'Inter', 'sans-serif'],
+        label: ['var(--font-inter)', 'Inter', 'sans-serif'],
+      },
+      borderRadius: {
+        DEFAULT: '4px',
+        sm: '2px',
+        md: '6px',
+        lg: '8px',
+      },
+    },
   },
   plugins: [require('@tailwindcss/forms')],
 };