Subscribe to Baileys `messages.reaction` events and surface them as
system events for the agent session. Follows the same pattern used by
Signal and Slack: listen → parse → route → enqueueSystemEvent.
- Add `WebInboundReaction` type and `onReaction` callback to monitor
- Parse emoji, sender JID, target message ID from Baileys event
- Route via `resolveAgentRoute` and enqueue as system event
- Handle self-reaction attribution (reactionKey.fromMe → selfJid)
- Skip reaction removals (empty emoji) and status/broadcast JIDs
- Outer + inner try/catch for resilience against malformed events
- 13 unit tests (monitor-level + system event wiring)
- Changelog entry and docs updates
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
