Enable demo mode features, auto-fill demo credentials, and enhance branding integration

- Added `DEMO_MODE` to backend configuration with relaxed security support for specific demo accounts.
- Updated password validators to allow predefined weak passwords in demo mode.
- Auto-fill login forms with demo credentials via query parameters for improved demo accessibility.
- Introduced demo user creation logic during database initialization if `DEMO_MODE` is enabled.
- Replaced `img` tags with `next/image` for consistent and optimized visuals in branding elements.
- Refined footer, header, and layout components to incorporate improved logo handling.

frontend/src/components/home/DemoCredentialsModal.tsx

@@ -141,12 +141,12 @@ export function DemoCredentialsModal({ open, onClose }: DemoCredentialsModalProp
         <DialogFooter>
           <div className="grid grid-cols-1 sm:grid-cols-2 gap-2 w-full">
             <Button asChild variant="default" className="w-full">
-              <Link href="/login" onClick={onClose}>
+              <Link href="/login?email=demo@example.com&password=Demo123!" onClick={onClose}>
                 Login as User
               </Link>
             </Button>
             <Button asChild variant="default" className="w-full">
-              <Link href="/login" onClick={onClose}>
+              <Link href="/login?email=admin@example.com&password=Admin123!" onClick={onClose}>
                 Login as Admin
               </Link>
             </Button>