Refactored resurrection functions to accept optional *sql.Conn parameter:
- Added tryResurrectParentWithConn() internal function
- Added tryResurrectParentChainWithConn() internal function
- Updated CreateIssue to use conn-based resurrection
- Updated EnsureIDs to use conn-based resurrection
This eliminates 'database is locked' errors when resurrection
happens inside an existing transaction.
Fixes bd-58c0
- Add GetNextChildID to storage interface for generating child IDs
- Implement in SQLiteStorage with atomic counter using child_counters table
- Implement in MemoryStorage with in-memory counter
- Add --parent flag to bd create command
- Support hierarchical IDs (bd-a3f8e9.1, bd-a3f8e9.1.5) in CreateIssue
- Validate parent exists when creating hierarchical issues
- Enforce max depth of 3 levels
- Update ID validation to accept hierarchical IDs with dots
- Add comprehensive tests for child ID generation
- Manual testing confirms: sequential children, nested hierarchies, depth enforcement
