v3.42.71: Fix error message formatting + code alignment

- Fixed incorrect diagnostic message for shared memory exhaustion
  (was 'Cannot access file', now 'PostgreSQL lock table exhausted')
- Improved clarity of lock capacity formula display
- Code formatting: aligned struct field comments for consistency
- Files affected: restore_exec.go, backup_exec.go, persist.go

internal/config/persist.go

@@ -30,7 +30,7 @@ type LocalConfig struct {
 	// Performance settings
 	CPUWorkload     string
 	MaxCores        int
-	ClusterTimeout  int  // Cluster operation timeout in minutes (default: 1440 = 24 hours)
+	ClusterTimeout  int // Cluster operation timeout in minutes (default: 1440 = 24 hours)
 	ResourceProfile string
 	LargeDBMode     bool // Enable large database mode (reduces parallelism, increases locks)