feat: add allowed_users/allowed_channels support to GatewayConfig (LINE/Telegram)

[chaodu-agent]

Problem

The [gateway] config section (used by LINE and Telegram) has no access control fields. Unlike [discord] and [slack] which support allowed_users, allowed_channels, allow_all_users, and allow_all_channels, the gateway adapter accepts messages from any user in any chat with no filtering.

This means anyone who adds the LINE bot as a friend (or joins a group with it) can interact with the agent without restriction.

Proposed Solution

Add the same access control pattern used by Discord/Slack to GatewayConfig:

[gateway]
url = "ws://gateway:8080/ws"
platform = "line"
# allow_all_users = true
# allowed_users = ["U1234"]
# allow_all_channels = true
# allowed_channels = ["C5678"]

Implementation:

1. Add allow_all_users, allowed_users, allow_all_channels, allowed_channels fields to GatewayConfig in config.rs
2. Add filtering logic in gateway.rs message handler using the existing resolve_allow_all() helper
3. Update config.toml.example and docs/line.md

This reuses the existing resolve_allow_all() pattern — non-empty list auto-detects as restricted, empty list auto-detects as allow-all.

[github-actions]

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