feat(acp): surface Claude API retry state in chat input

Enable raw Claude SDK forwarding for ACP sessions and emit only system/api_retry events to the frontend.

Show a localized single-line retry banner with loading under the conversation input, including error details and retry progress.

src/lib/types.ts

@@ -362,6 +362,12 @@ export interface SessionUsageUpdateInfo {
 export type AcpEvent =
   | { type: "content_delta"; connection_id: string; text: string }
   | { type: "thinking"; connection_id: string; text: string }
+  | {
+      type: "claude_sdk_message"
+      connection_id: string
+      session_id: string
+      message: unknown
+    }
   | {
       type: "tool_call"
       connection_id: string