feat: 支持主动发送消息和附件处理

新增 `sendProactiveC2CMessage` 和 `sendProactiveGroupMessage` API，支持无需 msg_id 的主动消息发送（有月限额）。在网关中增加附件处理逻辑，支持解析图片和普通附件，并将附件信息传递给上下文。同时优化了 `sendText` 的目标地址解析逻辑，支持 `group:` 和 `channel:` 前缀，并新增 `sendProactiveMessage` 方法。

src/outbound.ts

@@ -1,5 +1,12 @@
 import type { ResolvedQQBotAccount } from "./types.js";
-import { getAccessToken, sendC2CMessage, sendChannelMessage } from "./api.js";
+import { 
+  getAccessToken, 
+  sendC2CMessage, 
+  sendChannelMessage, 
+  sendGroupMessage,
+  sendProactiveC2CMessage,
+  sendProactiveGroupMessage,
+} from "./api.js";
 
 export interface OutboundContext {
   to: string;
@@ -17,7 +24,30 @@ export interface OutboundResult {
 }
 
 /**
- * 发送文本消息
+ * 解析目标地址
+ * 格式：
+ *   - openid (32位十六进制) -> C2C 单聊
+ *   - group:xxx -> 群聊
+ *   - channel:xxx -> 频道
+ *   - 纯数字 -> 频道
+ */
+function parseTarget(to: string): { type: "c2c" | "group" | "channel"; id: string } {
+  if (to.startsWith("group:")) {
+    return { type: "group", id: to.slice(6) };
+  }
+  if (to.startsWith("channel:")) {
+    return { type: "channel", id: to.slice(8) };
+  }
+  // openid 通常是 32 位十六进制
+  if (/^[A-F0-9]{32}$/i.test(to)) {
+    return { type: "c2c", id: to };
+  }
+  // 默认当作频道 ID
+  return { type: "channel", id: to };
+}
+
+/**
+ * 发送文本消息（被动回复，需要 replyToId）
  */
 export async function sendText(ctx: OutboundContext): Promise<OutboundResult> {
   const { to, text, replyToId, account } = ctx;
@@ -28,16 +58,53 @@ export async function sendText(ctx: OutboundContext): Promise<OutboundResult> {
 
   try {
     const accessToken = await getAccessToken(account.appId, account.clientSecret);
+    const target = parseTarget(to);
 
-    // 判断目标类型：openid (C2C) 或 channel_id (频道)
-    // openid 通常是 32 位十六进制，channel_id 通常是数字
-    const isC2C = /^[A-F0-9]{32}$/i.test(to);
-
-    if (isC2C) {
-      const result = await sendC2CMessage(accessToken, to, text, replyToId ?? undefined);
+    if (target.type === "c2c") {
+      const result = await sendC2CMessage(accessToken, target.id, text, replyToId ?? undefined);
+      return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
+    } else if (target.type === "group") {
+      const result = await sendGroupMessage(accessToken, target.id, text, replyToId ?? undefined);
       return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
     } else {
-      const result = await sendChannelMessage(accessToken, to, text, replyToId ?? undefined);
+      const result = await sendChannelMessage(accessToken, target.id, text, replyToId ?? undefined);
+      return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
+    }
+  } catch (err) {
+    const message = err instanceof Error ? err.message : String(err);
+    return { channel: "qqbot", error: message };
+  }
+}
+
+/**
+ * 主动发送消息（不需要 replyToId，有配额限制：每月 4 条/用户/群）
+ * 
+ * @param account - 账户配置
+ * @param to - 目标地址，格式：openid（单聊）或 group:xxx（群聊）
+ * @param text - 消息内容
+ */
+export async function sendProactiveMessage(
+  account: ResolvedQQBotAccount,
+  to: string,
+  text: string
+): Promise<OutboundResult> {
+  if (!account.appId || !account.clientSecret) {
+    return { channel: "qqbot", error: "QQBot not configured (missing appId or clientSecret)" };
+  }
+
+  try {
+    const accessToken = await getAccessToken(account.appId, account.clientSecret);
+    const target = parseTarget(to);
+
+    if (target.type === "c2c") {
+      const result = await sendProactiveC2CMessage(accessToken, target.id, text);
+      return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
+    } else if (target.type === "group") {
+      const result = await sendProactiveGroupMessage(accessToken, target.id, text);
+      return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
+    } else {
+      // 频道暂不支持主动消息，使用普通发送
+      const result = await sendChannelMessage(accessToken, target.id, text);
       return { channel: "qqbot", messageId: result.id, timestamp: result.timestamp };
     }
   } catch (err) {