T2.3: Split domain.Job (durable) from domain.JobRuntime (transient)

Move all transient execution state off domain.Job into a new
domain.JobRuntime, keyed by job ID:

- domain: Job now holds only durable YAML fields; remove the yaml:"-"
  fields (LastRun/NextRun/LastState/Logs/Output) and NextDue. Add
  runtime.go with JobRuntime plus NewRuntime/NewRuntimes constructors,
  which now own the runtime-init logic moved out of normalizeJobs.
- runner: RunJob no longer mutates the job; it is pure and returns the
  RunRecord for the caller to fold into the runtime.
- scheduler: take a shared map[int]*JobRuntime and route status/next-run
  bookkeeping through runtimeFor(job); prepareNextRun writes a *JobRuntime.
- storage: normalizeJobs touches only durable config.
- gui: own the runtime map (NewRuntimes), share it with the scheduler,
  and read/write runtime state via runtimeFor; maintain the map by ID on
  add/edit/delete.
- tests: update scheduler/storage tests to the split; tidy a pre-existing
  import-order nit in scheduler.go.

This also satisfies T2.4 (storage load/save only Job, runtime init in
domain.NewRuntime, round-trip tests), since removing the fields forced it.
Runtime-map ownership remains GUI-side glue until T3.1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/runner/runner.go

@@ -49,13 +49,14 @@ func RunJob(ctx context.Context, job *domain.Job, trigger string, logsDir string
 	}
 
 	now := time.Now()
-	job.LastRun = now.Format("2006-01-02 15:04:05")
-	job.LastState = state
-	job.Output = output
+	timestamp := now.Format("2006-01-02 15:04:05")
 	logFile := writeRunLog(logsDir, *job, trigger, state, detail, output, now)
 
-	record := domain.RunRecord{
-		Time:    job.LastRun,
+	// The runner is now pure with respect to the job: it returns a RunRecord and
+	// lets the caller fold that record into the job's JobRuntime. Run state no
+	// longer lives on Job, so there is nothing on the job to mutate here.
+	return domain.RunRecord{
+		Time:    timestamp,
 		JobID:   job.ID,
 		JobName: job.Name,
 		Trigger: trigger,
@@ -64,14 +65,6 @@ func RunJob(ctx context.Context, job *domain.Job, trigger string, logsDir string
 		LogFile: logFile,
 		Output:  output,
 	}
-	// Keep a small in-memory history for the currently running GUI. Full command
-	// output is persisted to files, so retaining every past record in RAM would
-	// only duplicate data and make long sessions grow without bound.
-	job.Logs = append([]domain.RunRecord{record}, job.Logs...)
-	if len(job.Logs) > 50 {
-		job.Logs = job.Logs[:50]
-	}
-	return record
 }
 
 func startJobOnly(invocation commandInvocation, job domain.Job, started time.Time) (string, string, string) {