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>

internal/storage/sqlite/transaction.go

@@ -305,7 +305,8 @@ func (t *sqliteTxStorage) GetIssue(ctx context.Context, id string) (*types.Issue
 		       status, priority, issue_type, assignee, estimated_minutes,
 		       created_at, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
-		       deleted_at, deleted_by, delete_reason, original_type
+		       deleted_at, deleted_by, delete_reason, original_type,
+		       sender, ephemeral, replies_to, relates_to, duplicate_of, superseded_by
 		FROM issues
 		WHERE id = ?
 	`, id)
@@ -1084,7 +1085,8 @@ func (t *sqliteTxStorage) SearchIssues(ctx context.Context, query string, filter
 		       status, priority, issue_type, assignee, estimated_minutes,
 		       created_at, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
-		       deleted_at, deleted_by, delete_reason, original_type
+		       deleted_at, deleted_by, delete_reason, original_type,
+		       sender, ephemeral, replies_to, relates_to, duplicate_of, superseded_by
 		FROM issues
 		%s
 		ORDER BY priority ASC, created_at DESC
@@ -1124,6 +1126,13 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 	var deletedBy sql.NullString
 	var deleteReason sql.NullString
 	var originalType sql.NullString
+	// Messaging fields (bd-kwro)
+	var sender sql.NullString
+	var ephemeral sql.NullInt64
+	var repliesTo sql.NullString
+	var relatesTo sql.NullString
+	var duplicateOf sql.NullString
+	var supersededBy sql.NullString
 
 	err := row.Scan(
 		&issue.ID, &contentHash, &issue.Title, &issue.Description, &issue.Design,
@@ -1132,6 +1141,7 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 		&issue.CreatedAt, &issue.UpdatedAt, &closedAt, &externalRef,
 		&issue.CompactionLevel, &compactedAt, &compactedAtCommit, &originalSize, &sourceRepo, &closeReason,
 		&deletedAt, &deletedBy, &deleteReason, &originalType,
+		&sender, &ephemeral, &repliesTo, &relatesTo, &duplicateOf, &supersededBy,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to scan issue: %w", err)
@@ -1178,6 +1188,25 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 	if originalType.Valid {
 		issue.OriginalType = originalType.String
 	}
+	// Messaging fields (bd-kwro)
+	if sender.Valid {
+		issue.Sender = sender.String
+	}
+	if ephemeral.Valid && ephemeral.Int64 != 0 {
+		issue.Ephemeral = true
+	}
+	if repliesTo.Valid {
+		issue.RepliesTo = repliesTo.String
+	}
+	if relatesTo.Valid && relatesTo.String != "" {
+		issue.RelatesTo = parseJSONStringArray(relatesTo.String)
+	}
+	if duplicateOf.Valid {
+		issue.DuplicateOf = duplicateOf.String
+	}
+	if supersededBy.Valid {
+		issue.SupersededBy = supersededBy.String
+	}
 
 	return &issue, nil
 }