Fix stale nav after login/register: use full page navigation

goto() does client-side navigation which caches the layout data
(user is still null). Using window.location.href forces a full
server round-trip so the nav bar reflects the authenticated user.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/routes/auth/login/+page.svelte

@@ -1,6 +1,4 @@
 <script lang="ts">
-	import { goto } from '$app/navigation';
-
 	let email = $state('');
 	let password = $state('');
 	let error = $state('');
@@ -24,7 +22,7 @@
 				return;
 			}
 
-			goto('/boards');
+			window.location.href = '/boards';
 		} catch {
 			error = 'Network error. Please try again.';
 		} finally {

src/routes/auth/register/+page.svelte

@@ -1,6 +1,4 @@
 <script lang="ts">
-	import { goto } from '$app/navigation';
-
 	let name = $state('');
 	let email = $state('');
 	let password = $state('');
@@ -25,7 +23,7 @@
 				return;
 			}
 
-			goto('/boards');
+			window.location.href = '/boards';
 		} catch {
 			error = 'Network error. Please try again.';
 		} finally {