feat: detect reply/forward/crosspost in message capture + inject into AI moderation
- Add is_reply, is_forward, is_crosspost, reference_message_id,
reference_channel_id, reference_guild_id columns to messages table
- Update MessageRecord type with reference fields
- Extract reply/forward/crosspost from Discord message type/flags
- Track reference.type (DEFAULT=reply, FORWARD) and CROSSPOSTED flag
- Inject <reference> XML with parent content into LLM moderation prompt
- Add reply/forward/crosspost rules to moderation prompt rules
- Format context messages with [reply_to], [forward_from], [crosspost]
- Add migration 0009
Co-Authored-By: Claude <noreply@anthropic.com>