- Add NudgeChannels field to MessagingConfig struct in types.go
- Initialize NudgeChannels map in NewMessagingConfig()
- Add validation in validateMessagingConfig(): channel names must be
non-empty and each channel must have at least one recipient
- Add tests for valid nudge channels and empty recipient validation
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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