fix(auth): remove hardcoded light-mode Clerk appearance override on log-in/sign-up

SignIn/SignUp passed their own appearance.variables.colorBackground
("#FAFAFA", always light) and colorPrimary, which Clerk merges on top
of ClerkThemeProvider's appearance -- so in Dark Mode the provider's
baseTheme: dark (light-on-dark default text colors) stayed active
while colorBackground got forced back to light by the page-level
override. Light text on a light background made the whole form
unreadable.

Both page-level appearance props now only set elements.formButtonPrimary
(the orange CTA, theme-independent) -- colorPrimary/colorBackground are
already handled correctly, theme-aware, by ClerkThemeProvider.

src/app/(auth)/log-in/[[...sign-in]]/page.tsx

@@ -17,10 +17,6 @@ export default function LogInPage() {
       signUpUrl="/sign-up"
       forceRedirectUrl="/pets"
       appearance={{
-        variables: {
-          colorPrimary: "#F97316",
-          colorBackground: "#FAFAFA",
-        },
         elements: {
           formButtonPrimary:
             "bg-orange-500 hover:bg-orange-600 text-white text-sm",

src/app/(auth)/sign-up/[[...sign-up]]/page.tsx

@@ -17,10 +17,6 @@ export default function SignUpPage() {
       signInUrl="/log-in"
       forceRedirectUrl="/onboarding/pet"
       appearance={{
-        variables: {
-          colorPrimary: "#F97316",
-          colorBackground: "#FAFAFA",
-        },
         elements: {
           formButtonPrimary:
             "bg-orange-500 hover:bg-orange-600 text-white text-sm",