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_form.go

@@ -111,6 +111,7 @@ func CreateIssueFromFormValues(ctx context.Context, s storage.Storage, fv *creat
 		IssueType:          types.IssueType(fv.IssueType),
 		Assignee:           fv.Assignee,
 		ExternalRef:        externalRefPtr,
+		CreatedBy:          getActorWithGit(), // GH#748: track who created the issue
 	}
 
 	// Check if any dependencies are discovered-from type