feat: Settings in Datenbank speichern statt localStorage

- Neue Spalte 'settings' in users-Tabelle (Migration via TryAddColumn)
- SettingsEndpoint: GET/PUT /api/settings
- DatabaseService: GetUserSettings() + UpdateUserSettings()
- Frontend: currentSettings als globaler State in app.js
- settings-page.js: localStorage komplett entfernt, nutzt API
- Settings werden beim App-Start aus DB geladen und angewendet

wwwroot/js/app.js

@@ -1,5 +1,28 @@
-// ── Global User State ──
+// ── Global State ──
 var currentUser = null;
+var currentSettings = null;
+
+const SETTINGS_DEFAULTS = {
+  pageWidth: 900,
+  toolCallDisplay: 'modifications',
+  chainMetaDisplay: 'sometimes',
+  showDeletedMessages: false
+};
+
+function loadSettings() {
+  return Object.assign({}, SETTINGS_DEFAULTS, currentSettings);
+}
+
+async function saveSettings(settings) {
+  currentSettings = settings;
+  applySettings();
+  try { await apiSaveSettings(settings); } catch (_) {}
+}
+
+function applySettings() {
+  var s = loadSettings();
+  document.documentElement.style.setProperty('--page-width', s.pageWidth + 'px');
+}
 
 // ── App Init ──
 
@@ -12,6 +35,8 @@ document.addEventListener('DOMContentLoaded', async () => {
   }
 
   currentUser = user;
+  currentSettings = await apiGetSettings();
+  applySettings();
   loadClaudeStatus();
 
   const { page, id } = parseHash();