Include all agents on heartbeats page regardless of interval config

Agents without a heartbeat interval configured (intervalSec=0) were
filtered out, making them invisible on the instance heartbeats page.
This prevented managing heartbeats for agents that hadn't been
configured yet (e.g. donchitos company agents).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/routes/agents.ts

@@ -901,7 +901,6 @@ export function agentRoutes(db: Db) {
         };
       })
       .filter((item) =>
-        item.intervalSec > 0 &&
         item.status !== "paused" &&
         item.status !== "terminated" &&
         item.status !== "pending_approval",