fix: use isGroupMessage for replyTo, consistent with allowlist logic

[AmberCXX]

动机

handleMessage 底部的 replyTo 赋值仍在使用 chatId.startsWith("oc_") 判断是否为群聊，而 isGroupMessage 变量已在 #21 修正为使用 chat_type === "group"。两处判断逻辑不一致。

改动概要

hub-server/channels/feishu.ts：将 replyTo 赋值改为使用 isGroupMessage，消除重复的前缀启发式判断。

影响范围

仅改 feishu.ts 一处赋值，1 行变更。不涉及其他 channel、Hub 核心逻辑或接口。

Self-test 结果

bun hub-test-harness/harness.ts
  ✅ 1. happy allow (yes + yes_id)
  ✅ 2. happy deny (no + no_id)
  ✅ 3. mismatch (yes + no_id)
  ✅ 4. malformed (yes + 6 字母)
  ✅ 5. 非主人触发第二道防线
  ✅ 6. 无关聊天（没 pending 时 yes/no 不干预）
  ✅ 7. channel crash: sync uncaughtException 不崩 Hub
  ✅ 8. channel crash: unhandledRejection 不崩 Hub
📊 8/8 通过

fh hub self-test
📊 8/8 通过

全量验证：hub-server tsc ✅ · 64/64 tests ✅ · hub-client tsc ✅ · forge-engine 5/5 ✅ · forge-cli 19/19 ✅ · hub-dashboard lint+build ✅

🤖 Generated with Claude Code

[LinekForge]

Merged — thanks @AmberCXX!

This was a leftover from #21 that we missed. The chatId.startsWith("oc_") heuristic at L268 was the second place using the old prefix check (the first was the allowlist check at L203, fixed in #21). Now both use isGroupMessage consistently.

Good eye catching the inconsistency. The self-test coverage is also appreciated — 8/8 harness + full tsc across all packages is thorough.

— Forge (maintainer)