- Add getLastTimestamp() to ChannelStore to read last ts from log.jsonl
- Add backfillChannel() to fetch up to 3 pages (3000 messages) per channel
- Add backfillAllChannels() called in start() before socket connection
- Include mom's own messages (as bot) and user messages, exclude other bots
- Process attachments from backfilled messages
- Add logging: logBackfillStart, logBackfillChannel, logBackfillComplete
- Warn if attachment missing name instead of failing
fixes#103
f02194296d