feat: refactor chat input handling and add BoardChatComposer component for improved chat functionality

frontend/src/components/BoardChatComposer.tsx

@@ -0,0 +1,57 @@
+"use client";
+
+import { memo, useCallback, useState } from "react";
+
+import { Button } from "@/components/ui/button";
+import { Textarea } from "@/components/ui/textarea";
+
+type BoardChatComposerProps = {
+  placeholder?: string;
+  isSending?: boolean;
+  onSend: (content: string) => Promise<boolean>;
+};
+
+function BoardChatComposerImpl({
+  placeholder = "Message the board lead. Tag agents with @name.",
+  isSending = false,
+  onSend,
+}: BoardChatComposerProps) {
+  const [value, setValue] = useState("");
+
+  const send = useCallback(async () => {
+    if (isSending) return;
+    const trimmed = value.trim();
+    if (!trimmed) return;
+    const ok = await onSend(trimmed);
+    if (ok) {
+      setValue("");
+    }
+  }, [isSending, onSend, value]);
+
+  return (
+    <div className="mt-4 space-y-2">
+      <Textarea
+        value={value}
+        onChange={(event) => setValue(event.target.value)}
+        onKeyDown={(event) => {
+          if (event.key !== "Enter") return;
+          if (event.nativeEvent.isComposing) return;
+          if (event.shiftKey) return;
+          event.preventDefault();
+          void send();
+        }}
+        placeholder={placeholder}
+        className="min-h-[120px]"
+        disabled={isSending}
+      />
+      <div className="flex justify-end">
+        <Button onClick={() => void send()} disabled={isSending || !value.trim()}>
+          {isSending ? "Sending…" : "Send"}
+        </Button>
+      </div>
+    </div>
+  );
+}
+
+export const BoardChatComposer = memo(BoardChatComposerImpl);
+BoardChatComposer.displayName = "BoardChatComposer";