fix: run paired DB writes sequentially to avoid hiding failed stages

Effect.all with concurrency: 2 uses fail-fast semantics, so when both
branches fail only one stage is reported. Remove the concurrency option
so operations run sequentially, ensuring the reported stage is always
deterministic and accurate.

Author: cursoragent

infra/relay/src/agentActivity/Devices.ts

@@ -118,7 +118,7 @@ export const make = Effect.gen(function* () {
                 )
             : Effect.void,
         ],
-        { concurrency: 2, discard: true },
+        { discard: true },
       );
 
       yield* db
@@ -209,7 +209,7 @@ export const make = Effect.gen(function* () {
               ),
             ),
         ],
-        { concurrency: 2, discard: true },
+        { discard: true },
       );
     }),
     listForUser: Effect.fn("relay.devices.listForUser")(function* (input) {