battery: send alerts on channel "testowy" (index 2), not the pinned send channel

Owner request. BatteryAlertService reads new env BATTERY_ALERT_CHANNEL
(default 2) at construction and passes it through MeshService.sendText,
which gains an optional trailing channel argument defaulting to the
pinned MESH_SEND_CHANNEL — every other sender is untouched. Threshold,
cooldown, merged one-message-per-cycle format and @mentions unchanged.

src/battery/battery.service.ts

@@ -33,6 +33,11 @@ export class BatteryAlertService {
     process.env.BATTERY_ALERT_COOLDOWN_MS ?? '21600000', // default 6 h
     10,
   );
+  // alerts ride "testowy" (index 2), not the pinned send channel — owner decision
+  private readonly alertChannel = parseInt(
+    process.env.BATTERY_ALERT_CHANNEL ?? '2',
+    10,
+  );
   // ponytail: in-memory cooldown map — resets on process restart (a node may get one duplicate alert after a deploy)
   private lastAlertAt = new Map<number, number>();
 
@@ -62,8 +67,13 @@ export class BatteryAlertService {
   }
 
   private async alert(nodes: NodeSummary[]): Promise<void> {
-    // one broadcast per cycle for the whole batch — never one message per node; rides the pinned send channel like every other bot send (MeshService.sendText)
-    await this.mesh.sendText(BROADCAST_ADDR, formatAlert(nodes));
+    // one broadcast per cycle for the whole batch — never one message per node; rides BATTERY_ALERT_CHANNEL ("testowy", default index 2) via the same MeshService.sendText path as every other bot send
+    await this.mesh.sendText(
+      BROADCAST_ADDR,
+      formatAlert(nodes),
+      undefined,
+      this.alertChannel,
+    );
     const now = Date.now();
     for (const n of nodes) this.lastAlertAt.set(n.num, now);
   }