feat: move reply/forward/flag/event buttons to plugin toolbar

- Toolbar now includes context-aware mail action buttons
- Reply, Forward, Flag, Create Event disabled when no mail selected
- Buttons grouped: account | search | compose | mail-actions | tools

frontend/src/pages/Mail.tsx

@@ -284,6 +284,7 @@ export function MailPage() {
   // Register toolbar items
   const { registerItems, unregisterPlugin } = usePluginToolbarStore();
   useEffect(() => {
+    const hasMail = !!selectedMail;
     registerItems('mail', [
       {
         id: 'account-select',
@@ -308,15 +309,52 @@ export function MailPage() {
         id: 'compose',
         plugin: 'mail',
         label: 'Verfassen',
-        group: 'actions',
+        group: 'compose',
         icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 4v16m8-8H4" /></svg>,
         onClick: handleCompose,
       },
+      {
+        id: 'reply',
+        plugin: 'mail',
+        label: 'Antworten',
+        group: 'mail-actions',
+        disabled: !hasMail,
+        icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M3 10h10a8 8 0 018 8v2M3 10l6 6m-6-6l6-6" /></svg>,
+        onClick: () => selectedMail && handleReply(selectedMail),
+      },
+      {
+        id: 'forward',
+        plugin: 'mail',
+        label: 'Weiterleiten',
+        group: 'mail-actions',
+        disabled: !hasMail,
+        icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M21 10H11a8 8 0 00-8 8v2m18-10l-6 6m6-6l-6-6" /></svg>,
+        onClick: () => selectedMail && handleForward(selectedMail),
+      },
+      {
+        id: 'flag',
+        plugin: 'mail',
+        label: 'Flagge',
+        group: 'mail-actions',
+        disabled: !hasMail,
+        active: selectedMail?.is_flagged,
+        icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M3 21v-4m0 0V5a2 2 0 012-2h6.5l1 1H21l-3 6 3 6h-8.5l-1-1H5a2 2 0 00-2 2zm9-13.5V9" /></svg>,
+        onClick: () => selectedMail && handleToggleFlag(selectedMail),
+      },
+      {
+        id: 'create-event',
+        plugin: 'mail',
+        label: 'Termin',
+        group: 'mail-actions',
+        disabled: !hasMail,
+        icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v12a2 2 0 002 2z" /></svg>,
+        onClick: () => selectedMail && handleCreateEvent(selectedMail),
+      },
       {
         id: 'sync',
         plugin: 'mail',
         label: 'Sync',
-        group: 'actions',
+        group: 'tools',
         icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M4 4v5h.582m15.356 2A8.001 8.001 0 004.582 9m0 0H9m11 11v-5h-.581m0 0a8.003 8.003 0 01-15.357-2m15.357 2H15" /></svg>,
         onClick: () => { /* sync trigger */ },
       },
@@ -324,13 +362,13 @@ export function MailPage() {
         id: 'settings',
         plugin: 'mail',
         label: 'Einstellungen',
-        group: 'actions',
+        group: 'tools',
         icon: <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M10.325 4.317c.426-1.756 2.924-1.756 3.35 0a1.724 1.724 0 002.573 1.066c1.543-.94 3.31.826 2.37 2.37a1.724 1.724 0 001.065 2.572c1.756.426 1.756 2.924 0 3.35a1.724 1.724 0 00-1.066 2.573c.94 1.543-.826 3.31-2.37 2.37a1.724 1.724 0 00-2.572 1.065c-.426 1.756-2.924 1.756-3.35 0a1.724 1.724 0 00-2.573-1.066c-1.543.94-3.31-.826-2.37-2.37a1.724 1.724 0 00-1.065-2.572c-1.756-.426-1.756-2.924 0-3.35a1.724 1.724 0 001.066-2.573c-.94-1.543.826-3.31 2.37-2.37.996.608 2.296.07 2.572-1.065z" /><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M15 12a3 3 0 11-6 0 3 3 0 016 0z" /></svg>,
         onClick: () => window.location.href = '/mail/settings',
       },
     ]);
     return () => unregisterPlugin('mail');
-  }, [registerItems, unregisterPlugin, accounts, selectedAccountId, handleAccountSwitch, handleSearch, handleCompose]);
+  }, [registerItems, unregisterPlugin, accounts, selectedAccountId, selectedMail, handleAccountSwitch, handleSearch, handleCompose, handleReply, handleForward, handleToggleFlag, handleCreateEvent]);
 
   if (loadingAccounts) {
     return (