feat: Add desktop screenshots

frontend/src/pages/GuidePage/sections/GettingStartedSection.tsx

@@ -32,7 +32,7 @@ export const GettingStartedSection = () => {
         />
 
         <GuideScreenshot
-          src="/guide/signup-desktop.webp"
+          src="/guide/signup-desktop.png"
           alt="Sign Up page with registration form"
           caption="The Sign Up form with email, password, and terms & conditions fields"
         />
@@ -66,7 +66,7 @@ export const GettingStartedSection = () => {
         </p>
 
         <GuideScreenshot
-          src="/guide/login-desktop.webp"
+          src="/guide/login-desktop.png"
           alt="Login page showing email and password entry"
           caption="The secure Auth0 login page"
         />
@@ -96,7 +96,7 @@ export const GettingStartedSection = () => {
         </ol>
 
         <GuideScreenshot
-          src="/guide/onboarding-desktop.webp"
+          src="/guide/onboarding-desktop.png"
           alt="Onboarding flow showing preferences step"
           caption="The onboarding flow guides new users through initial setup"
         />
@@ -116,7 +116,7 @@ export const GettingStartedSection = () => {
         </p>
 
         <GuideScreenshot
-          src="/guide/onboarding-mobile.webp"
+          src="/guide/onboarding-mobile.png"
           alt="Mobile onboarding showing vehicle setup step"
           caption="The onboarding flow is fully responsive and works on mobile devices"
           mobile