fix: resolve dev panel and CLI regressions

Synchronize scheduler concurrency across API and gRPC processes and restore persisted limits during recovery.

Serialize subscription mutations and preserve shared storage while cleaning Shell and CLI namespaces, historical references, and filesystem-specific naming candidates.

Handle CLI text responses correctly and include script history in backups. Add regression coverage for concurrency, cleanup ownership, long URLs, Unicode paths, and history exports.

back/protos/cron.proto

@@ -5,6 +5,7 @@ package com.ql.cron;
 service Cron {
   rpc addCron(AddCronRequest) returns (AddCronResponse);
   rpc delCron(DeleteCronRequest) returns (DeleteCronResponse);
+  rpc setConcurrency(SetConcurrencyRequest) returns (AddCronResponse);
 }
 
 message ISchedule { string schedule = 1; }
@@ -27,3 +28,6 @@ message AddCronResponse {}
 message DeleteCronRequest { repeated string ids = 1; }
 
 message DeleteCronResponse {}
+
+// Zero restores the default limit.
+message SetConcurrencyRequest { int32 concurrency = 1; }