feat(settings): fixed-height modal + move unlock sections to Account

- Centered settings modal gets a fixed height (min(88vh,620px)) so switching
  between short/long tabs no longer resizes + re-centers it. Entry #slideover
  stays content-sized (edit/new unaffected).
- PIN unlock / Quick unlock / Recovery key moved from Sécurité to the Account
  tab (unlock methods live with the account). Autofill stays in Sécurité.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.js

@@ -7813,8 +7813,8 @@ function closeSettings() {
 const SETTINGS_TAB_OF = {
     'Appearance': 'general',
     'Security': 'security', 'Clipboard privacy': 'security',
-    'PIN unlock': 'security', 'Quick unlock': 'security', 'Recovery key': 'security',
     'Account': 'account',
+    'PIN unlock': 'account', 'Quick unlock': 'account', 'Recovery key': 'account',
     'Export': 'sync', 'Sync (WebDAV)': 'sync', 'Auto-backup': 'sync', 'Import': 'sync',
 };
 let settingsActiveTab = 'general';