feat(settings): split Autofill into its own tab

Extracted the autofill toggle + hotkey combos out of the Security section into
their own .slideover-field labelled "Autofill", added an Autofill tab + map
entry. 5 tabs now.

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

index.html

@@ -417,6 +417,7 @@
         <div class="settings-tabs" id="settingsTabs">
             <button class="settings-tab is-active" data-tab="general">Général</button>
             <button class="settings-tab" data-tab="security">Sécurité</button>
+            <button class="settings-tab" data-tab="autofill">Autofill</button>
             <button class="settings-tab" data-tab="account">Account</button>
             <button class="settings-tab" data-tab="sync">Sync &amp; Backup</button>
         </div>
@@ -601,6 +602,9 @@
                         <span class="toggle-slider"></span>
                     </label>
                 </div>
+            </div>
+            <div class="slideover-field">
+                <div class="slideover-field-label">Autofill</div>
                 <div class="setting-row" id="settingAutofillRow">
                     <span>
                         Autofill with global hotkey