Feature/default messenger delivery target (openclaw#16985) thanks @KirillShchetinin

Verified:
- pnpm build
- pnpm check
- pnpm test:macmini

Co-authored-by: KirillShchetinin <13061871+KirillShchetinin@users.noreply.github.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/infra/outbound/targets.ts

@@ -169,20 +169,29 @@ export function resolveOutboundTarget(params: {
         })
       : undefined);
 
+  // Fall back to per-channel defaultTo when no explicit target is provided.
+  const effectiveTo =
+    params.to?.trim() ||
+    (params.cfg && plugin.config.resolveDefaultTo
+      ? plugin.config.resolveDefaultTo({
+          cfg: params.cfg,
+          accountId: params.accountId ?? undefined,
+        })
+      : undefined);
+
   const resolveTarget = plugin.outbound?.resolveTarget;
   if (resolveTarget) {
     return resolveTarget({
       cfg: params.cfg,
-      to: params.to,
+      to: effectiveTo,
       allowFrom,
       accountId: params.accountId ?? undefined,
       mode: params.mode ?? "explicit",
     });
   }
 
-  const trimmed = params.to?.trim();
-  if (trimmed) {
-    return { ok: true, to: trimmed };
+  if (effectiveTo) {
+    return { ok: true, to: effectiveTo };
   }
   const hint = plugin.messaging?.targetResolver?.hint;
   return {