feat: Wire up created_by field for beads issues (gt-u6nri)

- Add CreatedBy field to Issue struct (matches beads GH#748)
- Add Actor field to CreateOptions, pass --actor to bd create
- Add ActorString() method to RoleInfo for identity formatting
- Update all beads.Create() callers to pass Actor
- Update direct bd create exec calls with --actor:
  - mail/router.go: uses sender identity
  - patrol_helpers.go: uses role name
  - doctor/patrol_check.go: uses "gt-doctor"
  - rig/manager.go: uses "gt-rig-init"

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

internal/doctor/patrol_check.go

@@ -118,6 +118,7 @@ func (c *PatrolMoleculesExistCheck) Fix(ctx *CheckContext) error {
 				"--title="+mol,
 				"--description="+desc,
 				"--priority=2",
+				"--actor=gt-doctor",
 			)
 			cmd.Dir = rigPath
 			if err := cmd.Run(); err != nil {