feat(feishu): operator-configurable bot admission and mention policy

Add two operator-facing toggles for inbound Feishu admission, enabling
bot-to-bot scenarios such as A2A orchestration and inter-bot
notifications:

  FEISHU_ALLOW_BOTS=none|mentions|all   (default: none)
    Accept messages from other bots. `mentions` requires the peer
    bot to @-mention Hermes; `all` admits every peer-bot message.

  FEISHU_REQUIRE_MENTION=true|false     (default: true)
    Whether group messages must @-mention the bot. Override per-chat
    via `group_rules.<chat_id>.require_mention` in config.yaml.

Defaults preserve prior behavior. Self-echo protection is always on:
when the bot's identity is unresolved (auto-detection failed and
FEISHU_BOT_OPEN_ID unset), peer-bot messages are rejected fail-closed
to avoid feedback loops.

Admitted peer bots bypass the human-user allowlist
(FEISHU_ALLOWED_USERS) to match existing Discord behavior; humans
still need an explicit allowlist entry. yaml feishu.allow_bots is
bridged to the env var so the adapter and gateway auth layer share
one source of truth.

Resolving peer-bot display names requires the
application:bot.basic_info:read scope; without it, peers still route
but appear as their open_id.

Test: tests/gateway/test_feishu_bot_admission.py covers the admission
pipeline, group-policy bot-bypass, hydration, and event-dispatch
plumbing as a parametrized matrix.

Change-Id: I363cccb578c2a5c8b8bf0f0a890c01c89909e256

website/docs/reference/environment-variables.md

@@ -300,6 +300,8 @@ For cloud sandbox backends, persistence is filesystem-oriented. `TERMINAL_LIFETI
 | `FEISHU_ENCRYPT_KEY` | Optional encryption key for webhook mode |
 | `FEISHU_VERIFICATION_TOKEN` | Optional verification token for webhook mode |
 | `FEISHU_ALLOWED_USERS` | Comma-separated Feishu user IDs allowed to message the bot |
+| `FEISHU_ALLOW_BOTS` | `none` (default) / `mentions` / `all` — accept inbound messages from other bots. See [bot-to-bot messaging](../user-guide/messaging/feishu.md#bot-to-bot-messaging) |
+| `FEISHU_REQUIRE_MENTION` | `true` (default) / `false` — whether group messages must @mention the bot. Override per-chat via `group_rules.<chat_id>.require_mention`. |
 | `FEISHU_HOME_CHANNEL` | Feishu chat ID for cron delivery and notifications |
 | `WECOM_BOT_ID` | WeCom AI Bot ID from admin console |
 | `WECOM_SECRET` | WeCom AI Bot secret |