Fix signIn error swallowing — re-throw so LoginView shows the error

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

src/stores/auth.ts

@@ -46,6 +46,7 @@ export const useAuthStore = defineStore('auth', () => {
     } catch (e) {
       error.value = e instanceof Error ? e.message : String(e)
       loading.value = false
+      throw e
     }
   }
 

src/views/LoginView.vue

@@ -23,7 +23,7 @@
           />
         </div>
 
-        <p v-if="error" class="text-red-600 text-sm">{{ error }}</p>
+        <p v-if="error || auth.error" class="text-red-600 text-sm">{{ error || auth.error }}</p>
 
         <button
           type="submit"