feat(schema): add messaging fields for bd-kwro epic

- Add TypeMessage issue type for inter-agent communication
- Add 6 new Issue fields: Sender, Ephemeral, RepliesTo, RelatesTo,
  DuplicateOf, SupersededBy
- Add 4 new dependency types: replies-to, relates-to, duplicates, supersedes
- Create migration 019_messaging_fields with indexes
- Update all CRUD operations across storage layer
- Fix reset_test.go to use correct function names
- Fix redundant newline lint error in sync.go

Closes: bd-kwro.1

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/sync.go

@@ -2064,7 +2064,7 @@ type OrphanedChildren struct {
 // bd-hlsw.1: Detects forced pushes, prefix mismatches, and orphaned children.
 func showSyncIntegrityCheck(ctx context.Context, jsonlPath string) error {
 	fmt.Println("Sync Integrity Check")
-	fmt.Println("====================\n")
+	fmt.Println("====================")
 
 	result := &SyncIntegrityResult{}