Revert bd-191: Remove merged_into schema field

Use simpler approach for bd-190 merge feature:
- Close merged issues with reason 'Merged into bd-X'
- No schema changes or migrations needed
- Parseable close reason is cleaner than separate field

Also updated merge epic child issues with simplified design.

internal/storage/sqlite/dependencies.go

@@ -464,38 +464,38 @@ func (s *SQLiteStorage) GetDependencyTree(ctx context.Context, issueID string, m
 	rows, err := s.db.QueryContext(ctx, `
 		WITH RECURSIVE tree AS (
 			SELECT
-				i.id, i.title, i.status, i.priority, i.description, i.design,
-				i.acceptance_criteria, i.notes, i.issue_type, i.assignee,
-				i.estimated_minutes, i.created_at, i.updated_at, i.closed_at,
-				i.external_ref,
-				0 as depth,
-				i.id as path,
-				i.id as parent_id
+			i.id, i.title, i.status, i.priority, i.description, i.design,
+			i.acceptance_criteria, i.notes, i.issue_type, i.assignee,
+			i.estimated_minutes, i.created_at, i.updated_at, i.closed_at,
+			i.external_ref,
+			0 as depth,
+			i.id as path,
+			i.id as parent_id
 			FROM issues i
 			WHERE i.id = ?
 
 			UNION ALL
 
 			SELECT
-				i.id, i.title, i.status, i.priority, i.description, i.design,
-				i.acceptance_criteria, i.notes, i.issue_type, i.assignee,
-				i.estimated_minutes, i.created_at, i.updated_at, i.closed_at,
-				i.external_ref,
-				t.depth + 1,
-				t.path || '→' || i.id,
-				t.id
+			i.id, i.title, i.status, i.priority, i.description, i.design,
+			i.acceptance_criteria, i.notes, i.issue_type, i.assignee,
+			i.estimated_minutes, i.created_at, i.updated_at, i.closed_at,
+			i.external_ref,
+			t.depth + 1,
+			t.path || '→' || i.id,
+			t.id
 			FROM issues i
 			JOIN dependencies d ON i.id = d.depends_on_id
 			JOIN tree t ON d.issue_id = t.id
 			WHERE t.depth < ?
-			  AND t.path NOT LIKE '%' || i.id || '%'
-		)
-		SELECT id, title, status, priority, description, design,
-		       acceptance_criteria, notes, issue_type, assignee,
-		       estimated_minutes, created_at, updated_at, closed_at,
-		       external_ref, depth, parent_id
-		FROM tree
-		ORDER BY depth, priority, id
+			AND t.path NOT LIKE '%' || i.id || '%'
+			)
+			SELECT id, title, status, priority, description, design,
+			acceptance_criteria, notes, issue_type, assignee,
+			estimated_minutes, created_at, updated_at, closed_at,
+			external_ref, depth, parent_id
+			FROM tree
+			ORDER BY depth, priority, id
 	`, issueID, maxDepth)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get dependency tree: %w", err)

internal/storage/sqlite/sqlite.go

@@ -436,6 +436,8 @@ func migrateCompactedAtCommitColumn(db *sql.DB) error {
 	return nil
 }
 
+
+
 // getNextIDForPrefix atomically generates the next ID for a given prefix
 // Uses the issue_counters table for atomic, cross-process ID generation
 func (s *SQLiteStorage) getNextIDForPrefix(ctx context.Context, prefix string) (int, error) {

internal/types/types.go

@@ -27,7 +27,7 @@ type Issue struct {
 	CompactedAt        *time.Time     `json:"compacted_at,omitempty"`
 	CompactedAtCommit  *string        `json:"compacted_at_commit,omitempty"` // Git commit hash when compacted
 	OriginalSize       int            `json:"original_size,omitempty"`
-	Labels             []string       `json:"labels,omitempty"`       // Populated only for export/import
+	Labels             []string       `json:"labels,omitempty"` // Populated only for export/import
 	Dependencies       []*Dependency  `json:"dependencies,omitempty"` // Populated only for export/import
 	Comments           []*Comment     `json:"comments,omitempty"`     // Populated only for export/import
 }