feat: add ErrorNotification component and API error handling in Nuisance form

- Add ts/rmo/components/ErrorNotification.vue — reusable error alert
  with dismiss support, accessible markup, and configurable message
- Replace inline error div in Nuisance.vue with ErrorNotification
- Add resp.ok check in doSubmit() so HTTP error responses are caught
  and the workflow stops instead of proceeding to /submitted
- Fix typo: borwser → browser

Issue: #8

ts/rmo/components/ErrorNotification.vue

@@ -0,0 +1,81 @@
+<style scoped>
+.error-notification {
+    background-color: #f8d7da;
+    border: 1px solid #f5c6cb;
+    border-radius: 0.375rem;
+    padding: 1rem 1.25rem;
+    margin-bottom: 1rem;
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+}
+.error-icon {
+    font-size: 1.25rem;
+    flex-shrink: 0;
+}
+.error-text {
+    color: #721c24;
+    flex: 1;
+}
+.error-dismiss {
+    background: none;
+    border: none;
+    color: #721c24;
+    font-size: 1.25rem;
+    cursor: pointer;
+    padding: 0 0.25rem;
+    line-height: 1;
+    opacity: 0.7;
+}
+.error-dismiss:hover {
+    opacity: 1;
+}
+</style>
+
+<template>
+    <div v-if="visible" class="error-notification" role="alert">
+        <span class="error-icon" aria-hidden="true">✗</span>
+        <span class="error-text">{{ message }}</span>
+        <button
+            v-if="dismissible"
+            type="button"
+            class="error-dismiss"
+            aria-label="Dismiss error"
+            @click="dismiss"
+        >
+            ×
+        </button>
+    </div>
+</template>
+
+<script setup lang="ts">
+import { ref } from "vue";
+
+const props = withDefaults(
+    defineProps<{
+        message?: string;
+        dismissible?: boolean;
+    }>(),
+    {
+        message: "Something went wrong. Your request could not be completed. Please try again.",
+        dismissible: true,
+    },
+);
+
+const emit = defineEmits<{
+    dismissed: [];
+}>();
+
+const visible = ref(true);
+
+function dismiss() {
+    visible.value = false;
+    emit("dismissed");
+}
+
+function show() {
+    visible.value = true;
+}
+
+defineExpose({ show, dismiss });
+</script>