feat(feishu): add per-group require_mention flag

[JerryRobocat]

Summary

Adds an opt-in require_mention: false per-group setting for Feishu group rules. When set, the bot processes every message in that group without requiring an @mention — useful for solo bot-user groups or dedicated topic channels where you want DM-like behaviour without the ceremony of @-mentioning the bot every message.

Default remains True, so existing team/multi-person groups keep the safe mention-gated behaviour unchanged.

Motivation

In Feishu, group chats require an explicit @mention of the bot for messages to reach the agent — this is the correct default for shared/team groups. But users often want dedicated topic channels (just themselves + the bot) to organise parallel conversations on different projects. In those solo-with-bot groups, having to @-mention the bot for every single message is friction-heavy.

This change lets users opt specific groups out of the mention gate via a single config flag, while keeping the default safe for all existing groups.

Changes

• FeishuGroupRule dataclass gains a require_mention: bool = True field
• FeishuAdapter._load_settings() parses the new field from group_rules config
• _should_accept_group_message() checks the flag after the policy gate and bypasses mention checking when opted out
• The policy/allowlist/blacklist gate still applies — a blacklisted sender is still rejected even when mention gating is off
• New test covers the opt-in bypass, default-gated groups, and blacklist-still-applies cases

Example config

feishu:
  group_rules:
    oc_solo_topic:
      policy: open
      require_mention: false  # bot reads every message
    oc_team_chat:
      policy: open            # require_mention defaults to true

Tests

• tests/gateway/test_feishu.py::FeishuAdapterTests::test_per_group_require_mention_false_bypasses_mention_gate (new)
• Full tests/gateway/test_feishu.py suite: 107 passed
• Targeted group-gate tests: 13 passed

[JerryRobocat]

Closing for now — going to soak this locally for a few days before re-opening once the behaviour is polished. Local patch is staying applied on my machine to exercise it in real use.