feat: warn about unsupported attachment inputs

Compare normalized attachment MIME types with the selected model's declared input modalities and show a non-blocking warning for incompatible files.

Recheck newly added attachments, restored drafts, async metadata, and existing files after model changes while avoiding warnings when capability metadata is unavailable. Summarize affected filenames and localize the warning across every supported locale.

Add focused modality compatibility coverage, document the composer behavior, and keep model metadata subscriptions stable to prevent startup render loops.

packages/ui/src/lib/i18n/messages/ko.ts

@@ -2002,6 +2002,7 @@ export const dict: Record<I18nKey, string> = {
   'chat.chatInput.toast.addedFileMentions': '파일 멘션 {count}개 추가됨',
   'chat.chatInput.toast.attachFileFailed': '첨부 파일 실패',
   'chat.chatInput.toast.attachNamedFailed': '첨부 {name} 실패',
+  'chat.chatInput.toast.unsupportedAttachmentModalities': '{model}은(는) {files}에 필요한 {modalities} 입력을 지원하지 않습니다. 메시지를 보낼 수는 있지만 해당 첨부 파일이 무시될 수 있습니다.',
   'chat.chatInput.toast.someFilesSkipped': '일부 파일을 건너뛰었습니다:\n{summary}',
   'chat.chatInput.toast.vscodePickFailed': 'VS Code에서 파일 선택에 실패했습니다',
   'chat.chatInput.toast.openSessionFirst': '먼저 세션을 여세요',