fix: add interactions.jsonl to .gitignore allowlist

The interactions.jsonl file is an append-only audit log that should be
tracked in git (synced with bd sync), but it was missing from the
negation patterns in .beads/.gitignore.

This adds !interactions.jsonl alongside !issues.jsonl and !metadata.json
for consistency and clarity that this file should be committed.

Co-authored-by: Christian Catalan <crcatala@gmail.com>

cmd/bd/doctor/gitignore.go

@@ -37,6 +37,7 @@ beads.right.meta.json
 
 # Keep JSONL exports and config (source of truth for git)
 !issues.jsonl
+!interactions.jsonl
 !metadata.json
 !config.json
 `