Add IsLocked to ResolvedNativeAlarmSource; FlatteningService skips overrides on a
locked source (mirrors attribute/alarm lock rules); ManagementActor SetInstanceNativeAlarmSourceOverride
flattens the instance and rejects an override on a locked source (and rejects a
canonical name that does not resolve, preventing dangling overrides).
Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj
Spec promised a per-script timeout but only the global ScriptExecutionTimeoutSeconds
existed. Add nullable TemplateScript.ExecutionTimeoutSeconds threaded through EF +
flattening (ResolvedScript) to ScriptExecutionActor/AlarmExecutionActor, which use
perScript ?? global for the execution CTS. Includes the EF migration for the new column.