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/composables/useAuth.ts

@@ -13,19 +13,26 @@ export function useAuth() {
   const { loggedIn, user, clear, fetch } = useUserSession()
 
   /**
-   * Login with email
-   * Initiates OAuth2 flow
+   * Login with email and password
+   * Direct authentication via Cidaas API (no redirect)
    */
-  async function login(email: string) {
+  async function login(email: string, password: string) {
     try {
-      // Call login endpoint to get redirect URL
-      const { redirectUrl } = await $fetch('/api/auth/login', {
+      // Call login endpoint - creates session directly
+      await $fetch('/api/auth/login', {
         method: 'POST',
-        body: { email },
+        body: { email, password },
       })
 
-      // Redirect to Cidaas
-      navigateTo(redirectUrl, { external: true })
+      // Refresh user session
+      await fetch()
+
+      // Redirect to homepage or saved destination
+      const redirectAfterLogin = useCookie('redirect_after_login')
+      const destination = redirectAfterLogin.value || '/'
+      redirectAfterLogin.value = null // Clear cookie
+
+      navigateTo(destination)
     } catch (error) {
       console.error('Login failed:', error)
       throw error