fix: prevent [object Object] rendering in 25 frontend components

Replace direct {error} JSX rendering with typeof check + .message fallback.
When error is an object (not a string), React showed [object Object].
Now renders error.message or fallback string.

frontend/src/pages/AISettings.tsx

@@ -49,7 +49,7 @@ function ProviderTab() {
         <h2 className="text-lg font-semibold">Anbieter</h2>
         <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', provider_type: 'openai', api_key: '', base_url: '', is_default: false }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg hover:bg-primary-700">+ Hinzufügen</button>
       </div>
-      {error && <div className="text-sm text-red-600">{error}</div>}
+      {error && <div className="text-sm text-red-600">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
       {showForm && (
         <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
           <div className="grid grid-cols-2 gap-3">
@@ -134,7 +134,7 @@ function PresetTab() {
         <h2 className="text-lg font-semibold">Modelle & Presets</h2>
         <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', model_id: '', provider_id: '', temperature: 0.7, max_tokens: 2048, top_p: 1.0, system_prompt: '' }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">+ Hinzufügen</button>
       </div>
-      {error && <div className="text-sm text-red-600">{error}</div>}
+      {error && <div className="text-sm text-red-600">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
       {showForm && (
         <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
           <div className="grid grid-cols-2 gap-3">
@@ -225,7 +225,7 @@ function AgentTab() {
         <h2 className="text-lg font-semibold">Agenten</h2>
         <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', description: '', system_prompt: '', preset_id: '', tool_ids: [] }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">+ Hinzufügen</button>
       </div>
-      {error && <div className="text-sm text-red-600">{error}</div>}
+      {error && <div className="text-sm text-red-600">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
       {showForm && (
         <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
           <div className="grid grid-cols-2 gap-3">
@@ -291,7 +291,7 @@ function ToolsTab() {
     <div className="space-y-4">
       <h2 className="text-lg font-semibold">Verfügbare Tools</h2>
       <p className="text-sm text-secondary-500">Diese Tools werden von Plugins bereitgestellt und können Agenten zugewiesen werden.</p>
-      {error && <div className="text-sm text-red-600">{error}</div>}
+      {error && <div className="text-sm text-red-600">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
       {tools.length === 0 ? (
         <div className="text-sm text-secondary-400 py-8 text-center">Keine Tools verfügbar. Plugins können Tools registrieren.</div>
       ) : (

frontend/src/pages/Calendar.tsx

@@ -555,7 +555,7 @@ export function CalendarPage() {
     <div className="flex flex-col h-full" data-testid="calendar-page">
       {error && (
         <div className="mb-2 p-3 bg-danger-50 border border-danger-200 rounded-md" role="alert" data-testid="calendar-error">
-          <p className="text-sm text-danger-700">{error}</p>
+          <p className="text-sm text-danger-700">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</p>
         </div>
       )}
 

frontend/src/pages/CalendarKanban.tsx

@@ -98,7 +98,7 @@ export function CalendarKanbanPage() {
           className="mb-3 text-sm text-danger-700 bg-danger-50 border border-danger-200 rounded-md p-2"
           data-testid="kanban-error"
         >
-          {error}
+          {typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}
         </div>
       )}
 

frontend/src/pages/Communication.tsx

@@ -501,7 +501,7 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
           </div>
         )}
         {error && (
-          <div className="text-sm text-red-600 bg-red-50 rounded p-3">{error}</div>
+          <div className="text-sm text-red-600 bg-red-50 rounded p-3">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>
         )}
         {!loading && messages.length === 0 && !aiStreaming && (
           <div className="text-center text-secondary-400 py-8">

frontend/src/pages/DmsTrash.tsx

@@ -114,7 +114,7 @@ export function DmsTrashPage() {
       <div className="p-6 max-w-7xl mx-auto" data-testid="dms-trash-page">
         <EmptyState
           title={t('dms.error')}
-          description={error}
+          description={typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}
           action={<Button onClick={() => window.location.reload()}>{t('dms.cancel')}</Button>}
         />
       </div>

frontend/src/pages/Mail.tsx

@@ -872,7 +872,7 @@ export function MailPage() {
     <div className="flex flex-col h-full" data-testid="mail-page">
       {error && (
         <div className="mb-2 p-3 bg-danger-50 border border-danger-200 rounded-md" role="alert" data-testid="mail-error">
-          <p className="text-sm text-danger-700">{error}</p>
+          <p className="text-sm text-danger-700">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</p>
         </div>
       )}
 

frontend/src/pages/SettingsCurrencies.tsx

@@ -116,7 +116,7 @@ export function SettingsCurrenciesPage() {
         </button>
       </div>
 
-      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{error}</div>}
+      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
 
       {showForm && (
         <form onSubmit={handleSubmit(onSubmit)} className="p-4 border border-secondary-200 rounded-lg space-y-3">

frontend/src/pages/SettingsSequences.tsx

@@ -115,7 +115,7 @@ export function SettingsSequencesPage() {
         </button>
       </div>
 
-      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{error}</div>}
+      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
 
       {showForm && (
         <form onSubmit={handleSubmit(onSubmit)} className="p-4 border border-secondary-200 rounded-lg space-y-3">

frontend/src/pages/SettingsTaxes.tsx

@@ -118,7 +118,7 @@ export function SettingsTaxesPage() {
         </button>
       </div>
 
-      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{error}</div>}
+      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
 
       {showForm && (
         <form onSubmit={handleSubmit(onSubmit)} className="p-4 border border-secondary-200 rounded-lg space-y-3">

frontend/src/pages/SettingsWebhooks.tsx

@@ -203,7 +203,7 @@ function WebhookFormModal({ open, onClose, webhook, onSubmit, isSubmitting, erro
         {/* Error */}
         {error && (
           <div className="rounded-md bg-danger-50 border border-danger-200 px-3 py-2 text-sm text-danger-700">
-            {error}
+            {typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}
           </div>
         )}
 

frontend/src/pages/Tags.tsx

@@ -135,7 +135,7 @@ function TagFormModal({ open, onClose, tag, onSubmit, isSubmitting, error }: Tag
         {/* Error */}
         {error && (
           <div className="rounded-md bg-danger-50 border border-danger-200 px-3 py-2 text-sm text-danger-700">
-            {error}
+            {typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}
           </div>
         )}