Implement direct login functionality with email and password

- Update login API to support direct authentication via email and password, removing the OAuth2 redirect flow.
- Modify LoginForm component to include password field and validation.
- Refactor useAuth composable to handle login with both email and password.
- Remove unnecessary OAuth2 callback handler and PKCE utilities.
- Update relevant documentation and error handling for the new login method.

app/pages/auth.vue

@@ -43,6 +43,8 @@ definePageMeta({
 </script>
 
 <template>
+  <CommonHeader />
+
   <div class="container mx-auto max-w-lg px-4 py-12 sm:py-16">
     <div class="mb-10 text-center">
       <h1 class="text-4xl font-light tracking-tight">
@@ -102,4 +104,6 @@ definePageMeta({
       </TabsContent>
     </Tabs>
   </div>
+
+  <CommonFooter />
 </template>