UI bug pass: fix settings crash and rename dead heading

- Rename "Chat Defaults" heading to "Defaults" in settings general
- Guard sw.api.models.enabled() call (crashes when no providers
  are configured since models API returns undefined)
- Verified: admin, settings, login surfaces render correctly in
  both light and dark themes at desktop viewport

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/js/sw/surfaces/settings/general.js

@@ -1,5 +1,5 @@
 /**
- * GeneralSection — chat defaults: model, system prompt, max tokens, temperature, thinking
+ * GeneralSection — user preferences (model, system prompt, max tokens, temperature)
  */
 const { html } = window;
 const { useState, useEffect, useCallback, useRef } = hooks;
@@ -15,10 +15,8 @@ export function GeneralSection() {
     useEffect(() => {
         (async () => {
             try {
-                const [s, m] = await Promise.all([
-                    sw.api.profile.settings(),
-                    sw.api.models.enabled(),
-                ]);
+                const s = await sw.api.profile.settings();
+                const m = sw.api.models?.enabled ? await sw.api.models.enabled() : null;
                 const sObj = s || {};
                 setSettings({
                     model: sObj.model || '',
@@ -27,7 +25,7 @@ export function GeneralSection() {
                     temperature: sObj.temperature ?? 0.7,
                     show_thinking: sObj.show_thinking || false,
                 });
-                const modelList = (m.data || []).filter(x => !x.hidden);
+                const modelList = (m?.data || []).filter(x => !x.hidden);
                 setModels(modelList);
 
                 // Set initial max hint
@@ -74,7 +72,7 @@ export function GeneralSection() {
 
     return html`
         <div class="settings-section">
-            <h3>Chat Defaults</h3>
+            <h3>Defaults</h3>
             <div class="form-group">
                 <label>Default Model</label>
                 <select value=${settings.model} onChange=${onModelChange}>