Replace "FastNext" branding with "PragmaStack" across the project

- Updated all references, metadata, and templates to reflect the new branding, including layout files, components, and documentation.
- Replaced hardcoded color tokens like `green-600` with semantic tokens (`success`, `warning`, etc.) for improved design consistency.
- Enhanced `globals.css` with new color tokens for success, warning, and destructive states using the OKLCH color model.
- Added comprehensive branding guidelines and updated the design system documentation to align with the new identity.
- Updated tests and mocks to reflect the branding changes and ensured all visual/verbal references match "PragmaStack".
- Added new `branding/README.md` and `branding` docs for mission, values, and visual identity definition.

frontend/src/lib/i18n/metadata.ts

@@ -13,8 +13,8 @@ export type Locale = 'en' | 'it';
  */
 export const siteConfig = {
   name: {
-    en: 'FastNext Template',
-    it: 'FastNext Template',
+    en: 'PragmaStack',
+    it: 'PragmaStack',
   },
   description: {
     en: 'Production-ready FastAPI + Next.js full-stack template with authentication, admin panel, and comprehensive testing',