fix: restrict file attachments to images only

The OpenClaw gateway only supports image attachments in chat.send;
non-image files were silently dropped, confusing users (fixes #24).

- Filter non-image files in addFiles handler
- Update file input accept to image/* only
- Remove unused fileToBase64 helper
- Update i18n labels from 'Attach file' to 'Attach image' (all 8 langs)

Fixes #24

src/lib/i18n.ts

@@ -49,7 +49,7 @@ const en = {
   'chat.loadingHistory': 'Loading messages…',
   'chat.inputPlaceholder': 'Type a message…',
   'chat.inputLabel': 'Message',
-  'chat.attachFile': 'Attach file',
+  'chat.attachFile': 'Attach image',
   'chat.send': 'Send',
   'chat.stop': 'Stop',
   'chat.showPreview': 'Preview markdown',
@@ -245,7 +245,7 @@ const fr: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'Chargement des messages…',
   'chat.inputPlaceholder': 'Tapez un message…',
   'chat.inputLabel': 'Message',
-  'chat.attachFile': 'Joindre un fichier',
+  'chat.attachFile': 'Joindre une image',
   'chat.send': 'Envoyer',
   'chat.stop': 'Arrêter',
   'chat.showPreview': 'Aperçu markdown',
@@ -428,7 +428,7 @@ const es: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'Cargando mensajes…',
   'chat.inputPlaceholder': 'Escribe un mensaje…',
   'chat.inputLabel': 'Mensaje',
-  'chat.attachFile': 'Adjuntar archivo',
+  'chat.attachFile': 'Adjuntar imagen',
   'chat.send': 'Enviar',
   'chat.stop': 'Detener',
   'chat.showPreview': 'Vista previa markdown',
@@ -613,7 +613,7 @@ const de: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'Nachrichten werden geladen…',
   'chat.inputPlaceholder': 'Nachricht eingeben…',
   'chat.inputLabel': 'Nachricht',
-  'chat.attachFile': 'Datei anhängen',
+  'chat.attachFile': 'Bild anhängen',
   'chat.send': 'Senden',
   'chat.stop': 'Stoppen',
   'chat.showPreview': 'Markdown-Vorschau',
@@ -796,7 +796,7 @@ const ja: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'メッセージを読み込み中…',
   'chat.inputPlaceholder': 'メッセージを入力…',
   'chat.inputLabel': 'メッセージ',
-  'chat.attachFile': 'ファイルを添付',
+  'chat.attachFile': '画像を添付',
   'chat.send': '送信',
   'chat.stop': '停止',
   'chat.showPreview': 'Markdownプレビュー',
@@ -979,7 +979,7 @@ const pt: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'Carregando mensagens…',
   'chat.inputPlaceholder': 'Digite uma mensagem…',
   'chat.inputLabel': 'Mensagem',
-  'chat.attachFile': 'Anexar arquivo',
+  'chat.attachFile': 'Anexar imagem',
   'chat.send': 'Enviar',
   'chat.stop': 'Parar',
   'chat.showPreview': 'Pré-visualizar markdown',
@@ -1162,7 +1162,7 @@ const zh: Record<keyof typeof en, string> = {
   'chat.loadingHistory': '加载消息中…',
   'chat.inputPlaceholder': '输入消息…',
   'chat.inputLabel': '消息',
-  'chat.attachFile': '添加附件',
+  'chat.attachFile': '添加图片',
   'chat.send': '发送',
   'chat.stop': '停止',
   'chat.showPreview': '预览 Markdown',
@@ -1345,7 +1345,7 @@ const it: Record<keyof typeof en, string> = {
   'chat.loadingHistory': 'Caricamento messaggi…',
   'chat.inputPlaceholder': 'Scrivi un messaggio…',
   'chat.inputLabel': 'Messaggio',
-  'chat.attachFile': 'Allega file',
+  'chat.attachFile': 'Allega immagine',
   'chat.send': 'Invia',
   'chat.stop': 'Ferma',
   'chat.showPreview': 'Anteprima markdown',