Extracted duplicated switch statement for mapping step type strings to
types.IssueType into a single helper function. This removes code
duplication between collectStepsToSubgraph() and collectStepsRecursive().
The new stepTypeToIssueType() function:
- Converts 'task', 'bug', 'feature', 'epic', 'chore' to types
- Returns types.TypeTask for empty or unrecognized types
- Used by both functions with children-override-to-epic logic preserved
f459f8ef7f