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/components/home/Header.tsx

@@ -32,7 +32,7 @@ export function Header({ onOpenDemoModal }: HeaderProps) {
           {/* Logo */}
           <Link href="/" className="font-bold text-xl hover:opacity-80 transition-opacity">
             <span className="bg-gradient-to-r from-primary to-primary/60 bg-clip-text text-transparent">
-              FastNext
+              PragmaStack
             </span>{' '}
             <span className="text-foreground">Template</span>
           </Link>