m4: settings-UI polish (dirty tracking + load-error state)

Save is disabled unless something actually changed (dirty = current values
vs. the last loaded/saved snapshot); "Saved." clears the moment you edit
again, and a quiet "No unsaved changes" shows at rest. A failed load now
renders an explicit error + Retry instead of a blank form.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/views/SettingsView.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { computed, onMounted, ref } from "vue";
+import { computed, onMounted, ref, watch } from "vue";
 import { api } from "../api/client";
 import { useConfigStore } from "../stores/config";
 import BaseButton from "../components/BaseButton.vue";
@@ -17,11 +17,18 @@ interface SettingItem {
 const config = useConfigStore();
 
 const items = ref<SettingItem[]>([]);
+const original = ref<Record<string, string | boolean | number>>({});
 const loading = ref(true);
 const saving = ref(false);
 const error = ref("");
 const saved = ref(false);
 
+// Unsaved-changes tracking: compare current values to the last loaded/saved snapshot.
+const dirty = computed(() => items.value.some((it) => it.value !== original.value[it.key]));
+watch(dirty, (d) => {
+  if (d) saved.value = false;
+});
+
 const groups = computed(() => {
   const map = new Map<string, SettingItem[]>();
   for (const it of items.value) {
@@ -32,11 +39,17 @@ const groups = computed(() => {
   return Array.from(map, ([name, entries]) => ({ name, entries }));
 });
 
+function snapshot(list: SettingItem[]) {
+  original.value = Object.fromEntries(list.map((it) => [it.key, it.value]));
+}
+
 async function load() {
   loading.value = true;
+  error.value = "";
   try {
     const res = await api.get<{ settings: SettingItem[] }>("/api/settings");
     items.value = res.settings;
+    snapshot(res.settings);
   } catch {
     error.value = "Could not load settings.";
   } finally {
@@ -53,6 +66,7 @@ async function save() {
   try {
     const res = await api.patch<{ settings: SettingItem[] }>("/api/settings", { settings: payload });
     items.value = res.settings;
+    snapshot(res.settings);
     saved.value = true;
     await config.reload(); // header/site name reflects changes immediately
   } catch (e) {
@@ -87,6 +101,18 @@ onMounted(load);
 
     <div v-if="loading" class="py-20 text-center text-sm text-neutral-400">Loading…</div>
 
+    <div v-else-if="error && !items.length" class="py-20 text-center">
+      <h2 class="text-lg font-semibold text-neutral-700 dark:text-neutral-200">Couldn't load settings</h2>
+      <p class="mt-1 text-sm text-neutral-400">{{ error }}</p>
+      <button
+        type="button"
+        class="mt-3 rounded-md border border-neutral-300 px-3 py-1.5 text-sm hover:bg-neutral-100 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand dark:border-neutral-700 dark:hover:bg-neutral-800"
+        @click="load"
+      >
+        Retry
+      </button>
+    </div>
+
     <form v-else class="flex flex-col gap-8" @submit.prevent="save">
       <section v-for="group in groups" :key="group.name" class="flex flex-col gap-5">
         <h2 class="text-xs font-semibold uppercase tracking-wide text-neutral-400">{{ group.name }}</h2>
@@ -127,8 +153,9 @@ onMounted(load);
       </section>
 
       <div class="flex items-center gap-3">
-        <BaseButton type="submit" :loading="saving">Save changes</BaseButton>
+        <BaseButton type="submit" :loading="saving" :disabled="!dirty">Save changes</BaseButton>
-        <span v-if="saved" class="text-sm text-green-600 dark:text-green-400">Saved.</span>
+        <span v-if="saved && !dirty" class="text-sm text-green-600 dark:text-green-400">Saved.</span>
+        <span v-else-if="!dirty && !error" class="text-sm text-neutral-400">No unsaved changes</span>
         <span v-if="error" class="text-sm text-red-600 dark:text-red-400">{{ error }}</span>
       </div>
     </form>