Summary

• add discord.listen_mode with all and mentions modes, defaulting to all
• add discord.ignore_replies_to_others to skip forwarding replies unless they target the bot
• keep Discord bridge defaults backward compatible while matching Slack listen_mode semantics

Testing

• /opt/homebrew/bin/go test ./internal/session -run 'Test(DiscordSettings_TOML|BridgeTemplate_DiscordConfigLoading|BridgeTemplate_DiscordListenModeSupport|BridgeTemplate_DiscordReplyFilterSupport|BridgeTemplate_DiscordHeartbeatNotification|BridgeTemplate_DiscordTypingIndicator|SlackSettings_TOML)'

Notes

• defaults remain backward compatible: listen_mode = "all", ignore_replies_to_others = false
• full go test ./internal/session/... still hits the pre-existing TestStatusCycle_ShellSessionWithCommand failure unrelated to this change