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/dev/DevLayout.tsx

@@ -95,7 +95,7 @@ export function DevLayout({ children }: DevLayoutProps) {
             {/* Left: Logo + Badge */}
             <div className="flex items-center gap-3 shrink-0">
               <Code2 className="h-5 w-5 text-primary" />
-              <h1 className="text-base font-semibold">FastNext</h1>
+              <h1 className="text-base font-semibold">PragmaStack</h1>
               <Badge variant="secondary" className="text-xs">
                 Dev
               </Badge>