P1.5: drop SuccessExitCodes field and exit-code flexibility

Remove the SuccessExitCodes field from domain.Job and every layer that
read or wrote it: runner/exitcodes.go (deleted), runner.go runStateDetail
simplified to 0=OK / non-zero=Failed, logfile.go, format.go, operations.go,
store.go, job_dialog.go, and jobs_view.go. Tests updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/domain/job.go

@@ -12,7 +12,6 @@ type Job struct {
 	Schedule         string `json:"schedule"`
 	Command          string `json:"command"`
 	Arguments        string `json:"arguments,omitempty"`
-	SuccessExitCodes string `json:"success_exit_codes,omitempty"`
 	StartOnly        bool   `json:"start_only,omitempty"`
 	Enabled          bool   `json:"enabled"`
 }