feat: Add created_by field to issues (GH#748)

Add a created_by field to track who created each issue, similar to how
comments have an author field.

- Add CreatedBy string field to Issue struct
- Add migration 029 to add created_by column to issues table
- Update all SELECT/INSERT/Scan statements across storage layer
- Populate created_by in bd create from actor chain
- Display created_by in bd show output

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

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

cmd/bd/create.go

@@ -268,6 +268,7 @@ var createCmd = &cobra.Command{
 			ExternalRef:        externalRefPtr,
 			EstimatedMinutes:   estimatedMinutes,
 			Wisp:               wisp,
+			CreatedBy:          getActorWithGit(), // GH#748: track who created the issue
 		}
 
 		ctx := rootCtx