fix(sqlite): update child_counters when explicit child IDs are created (GH#728)

When creating issues with explicit hierarchical IDs (e.g., bd-test.1, bd-test.2
via --id flag or import), the child_counters table was not being updated.
This caused GetNextChildID to return colliding IDs when later called with
--parent.

Changes:
- Add ensureChildCounterUpdatedWithConn() to update counter on explicit child creation
- Add ParseHierarchicalID() to extract parent and child number from IDs
- Update CreateIssue to call counter update after hierarchical ID validation
- Update EnsureIDs to call counter update when parent exists
- Add post-insert phase in batch operations to update counters after FK
  constraint can be satisfied
- Update tests to reflect new behavior where counter is properly initialized

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

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

internal/storage/sqlite/queries.go

@@ -190,6 +190,14 @@ func (s *SQLiteStorage) CreateIssue(ctx context.Context, issue *types.Issue, act
 				// Parent(s) not found in JSONL history - cannot proceed
 				return fmt.Errorf("parent issue %s does not exist and could not be resurrected from JSONL history", parentID)
 			}
+
+			// Update child_counters to prevent future ID collisions (GH#728 fix)
+			// When explicit child IDs are used, the counter must be at least the child number
+			if _, childNum, ok := ParseHierarchicalID(issue.ID); ok {
+				if err := ensureChildCounterUpdatedWithConn(ctx, conn, parentID, childNum); err != nil {
+					return fmt.Errorf("failed to update child counter: %w", err)
+				}
+			}
 		}
 	}