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

gateway/config.py

@@ -900,6 +900,12 @@ def load_gateway_config() -> GatewayConfig:
                 if "dm_mention_threads" in matrix_cfg and not os.getenv("MATRIX_DM_MENTION_THREADS"):
                     os.environ["MATRIX_DM_MENTION_THREADS"] = str(matrix_cfg["dm_mention_threads"]).lower()
 
+            # Feishu settings → env vars (env vars take precedence)
+            feishu_cfg = yaml_cfg.get("feishu", {})
+            if isinstance(feishu_cfg, dict):
+                if "allow_bots" in feishu_cfg and not os.getenv("FEISHU_ALLOW_BOTS"):
+                    os.environ["FEISHU_ALLOW_BOTS"] = str(feishu_cfg["allow_bots"]).lower()
+
     except Exception as e:
         logger.warning(
             "Failed to process config.yaml — falling back to .env / gateway.json values. "