feat: add cross-context messaging resolver

Co-authored-by: Thinh Dinh <tobalsan@users.noreply.github.com>

src/cli/program/message/register.broadcast.ts

@@ -0,0 +1,18 @@
+import type { Command } from "commander";
+import type { MessageCliHelpers } from "./helpers.js";
+
+export function registerMessageBroadcastCommand(message: Command, helpers: MessageCliHelpers) {
+  helpers
+    .withMessageBase(
+      message.command("broadcast").description("Broadcast a message to multiple targets"),
+    )
+    .requiredOption(
+      "--targets <target...>",
+      "Targets to broadcast to (repeatable, accepts names or ids)",
+    )
+    .option("--message <text>", "Message to send")
+    .option("--media <url>", "Media URL")
+    .action(async (options: Record<string, unknown>) => {
+      await helpers.runMessageAction("broadcast", options);
+    });
+}