Add smart ACK provider for WeChat MP replies

Replace fixed ackText with a rule-based AckProvider that picks
response templates by message type and intent (translate, summary,
rewrite, poster, ppt, mindmap, code, search, schedule). Pure sync,
zero I/O, auto-falls back to config.ackText on any error.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wechat/ack/ack-provider.mjs

@@ -0,0 +1,29 @@
+import { resolveIntent } from './ack-intent.mjs';
+import { selectBuilder } from './ack-builders.mjs';
+
+function readConfig(config) {
+  return {
+    randomEnabled: config?.ackRandomEnabled !== false,
+    nicknameEnabled: config?.ackNicknameEnabled !== false,
+  };
+}
+
+// intent: normalizeWechatInboundIntent output ({ msgType, agentText, ... })
+// nickname: resolved display name string (empty string if unavailable)
+// config: loadWechatMpConfig output (plus ackRandomEnabled, ackNicknameEnabled)
+// fallbackText: config.ackText — returned on any error
+export function buildAckText({ intent, nickname, config, fallbackText }) {
+  try {
+    const cfg = readConfig(config);
+    const ctx = {
+      msgType: String(intent?.msgType ?? 'text'),
+      nickname: String(nickname ?? ''),
+      intent: resolveIntent(intent?.msgType, intent?.agentText),
+      randomEnabled: cfg.randomEnabled,
+      nicknameEnabled: cfg.nicknameEnabled,
+    };
+    return selectBuilder(ctx).build(ctx);
+  } catch {
+    return fallbackText ?? '已收到，正在处理，完成后发到这里。';
+  }
+}