Adds support for separate replyToMode settings for DMs vs channels:
- Add channels.slack.dm.replyToMode for DM-specific threading
- Keep channels.slack.replyToMode as default for channels
- Add resolveSlackReplyToMode helper to centralize logic
- Pass chatType through threading resolution chain
Usage:
```json5
{
channels: {
slack: {
replyToMode: "off", // channels
dm: {
replyToMode: "all" // DMs always thread
}
}
}
}
```
When dm.replyToMode is set, DMs use that mode; channels use the
top-level replyToMode. Backward compatible when not configured.
- Updated message processing to include full message IDs alongside short IDs for better context resolution.
- Improved reply handling by caching inbound messages, allowing for accurate sender and body resolution without exposing dropped content.
- Adjusted tests to validate the new full ID properties and their integration into the message handling workflow.
