P2R-01 follow-up: WS-path tests + drop unused retention from backup dispatch

Adds p2r01_ws_test.go covering the two paths the original commit's
in-process tests couldn't reach without a live conn:

- maybeAutoInit dispatches command.run(init) on first hello when creds
  are bound, skips on second hello once a job row exists, and skips
  entirely when the host has no creds.
- dispatchScheduledJob iterates a schedule's source groups and emits
  one backup per group with the right Tag/Includes; persists job rows
  with actor_kind=schedule + scheduled_id; no-ops on a disabled
  schedule.

Drops RetentionPolicy from the per-group Run-now and schedule.fire
backup payloads — the agent's RunBackup ignores it (forget is the
only consumer). Adds Hub.Conn() so tests can grab the live *Conn
post-hello.

internal/server/http/schedule_push.go

@@ -183,14 +183,15 @@ func (s *Server) dispatchBackupForGroup(ctx context.Context, conn *ws.Conn, host
 			"schedule_id", scheduleID, "group", g.Name, "err", err)
 		return
 	}
-	retention, _ := json.Marshal(g.RetentionPolicy)
+	// Backup ignores RetentionPolicy — the forget cadence lives on
+	// host_repo_maintenance and is driven by the server-side ticker
+	// (P2R-06). Don't ship the field on backup dispatches.
 	env, err := api.Marshal(api.MsgCommandRun, jobID, api.CommandRunPayload{
-		JobID:           jobID,
-		Kind:            api.JobBackup,
-		Includes:        g.Includes,
-		Excludes:        g.Excludes,
-		Tag:             g.Name,
-		RetentionPolicy: retention,
+		JobID:    jobID,
+		Kind:     api.JobBackup,
+		Includes: g.Includes,
+		Excludes: g.Excludes,
+		Tag:      g.Name,
 	})
 	if err != nil {
 		slog.Warn("schedule.fire: marshal command.run",