battery: merge multiple low-battery nodes into one broadcast per cycle

Owner follow-up: 'if multiple ppl shows at once — merge messages to one'.
check() now collects every qualifying node (at/below threshold and not
within its per-node cooldown) and sends AT MOST ONE broadcast per cycle
containing all of them, recording the alert timestamp for each after
sending; nothing is sent when none qualify. Format: '⚠️ battery low:
@!<hex> (<name>) <X>%[, @!<hex> (<name>) <Y>%]' — single-node case uses
the same one-entry template. Cooldown semantics unchanged.

CHANGELOG.md

@@ -2,11 +2,11 @@
 
 ## v0.13.0 — 2026-09-25 12:34
 
-- New non-AI `src/battery` module: `BatteryAlertModule` + `BatteryAlertService`, wired into `app.module.ts` exactly like the weather module (ScheduleModule.forRoot() + MeshModule). Every `BATTERY_CHECK_INTERVAL_MS` ms (default 60000, read at construction) it scans the same node state that backs `GET /api/nodes` and broadcasts a single-packet alert for every node whose reported battery is at or below `BATTERY_ALERT_THRESHOLD` percent (default 20). The comparison is `<=` on purpose — a node sitting exactly at the threshold counts as low; tests pin this choice.
-- Alert format: `⚠️ @!<8-hex-lowercase-node-num> battery low: <X>% (<longName or shortName>)` — Meshtastic mention syntax (`@!` + zero-padded 8-char lowercase hex, e.g. `@!09a2b3c4`), always well under the ~190-char single-packet limit; the name part falls back longName → shortName and is omitted entirely when the node reported no name. Broadcasts ride the pinned send channel via the existing `MeshService.sendText(BROADCAST_ADDR, text)` path (MESH_SEND_CHANNEL, default index 3) — no new transport.
-- Anti-spam: per-node cooldown of `BATTERY_ALERT_COOLDOWN_MS` ms (default 21600000 = 6 h) in an in-memory `Map<nodeNum, lastAlertEpochMs>` — a node is alerted at most once per window; the map resets on process restart by design (a node may get one duplicate alert after a deploy).
+- New non-AI `src/battery` module: `BatteryAlertModule` + `BatteryAlertService`, wired into `app.module.ts` exactly like the weather module (ScheduleModule.forRoot() + MeshModule). Every `BATTERY_CHECK_INTERVAL_MS` ms (default 60000, read at construction) it scans the same node state that backs `GET /api/nodes` and collects every node whose reported battery is at or below `BATTERY_ALERT_THRESHOLD` percent (default 20); when any qualify it sends AT MOST ONE broadcast per cycle containing all of them — never one message per node, and nothing at all when none qualify. The comparison is `<=` on purpose — a node sitting exactly at the threshold counts as low; tests pin this choice.
+- Alert format: `⚠️ battery low: @!<8-hex-lowercase-node-num> (<longName or shortName>) <X>%` with additional nodes appended as `, @!<hex> (<name>) <Y>%` (the single-node case is the same template with one entry) — Meshtastic mention syntax (`@!` + zero-padded 8-char lowercase hex, e.g. `@!09a2b3c4`), entries kept tight so common cases stay near the ~190-char single-packet limit; the name part falls back longName → shortName and is omitted entirely when a node reported no name. Broadcasts ride the pinned send channel via the existing `MeshService.sendText(BROADCAST_ADDR, text)` path (MESH_SEND_CHANNEL, default index 3) — no new transport.
+- Anti-spam: per-node cooldown of `BATTERY_ALERT_COOLDOWN_MS` ms (default 21600000 = 6 h) in an in-memory `Map<nodeNum, lastAlertEpochMs>` — only nodes outside their window are included in a batch and the alert timestamp is recorded for every node in it after sending, so a node is alerted at most once per window; the map resets on process restart by design (a node may get one duplicate alert after a deploy).
 - Live battery updates: `batteryLevel` was previously only populated from NodeInfo frames during the initial sync. Live NODEINFO_APP packets (port 4, serialized meshtastic.NodeInfo in Data.payload) now update `deviceMetrics` in the node database too — new `decodeNodeInfo()` + `PORT_NODEINFO_APP` in codec.ts, one branch in the existing packet-handling path — so alerts and `/api/nodes` reflect current values between syncs. Unknown nodes get a stub entry when they report metrics live; malformed payloads are skipped like every other port.
-- Tests: new `src/battery/battery.service.spec.ts` (mention hex padding/lowercase, full message construction incl. name fallbacks and the 190-char ceiling, threshold boundary with default + custom env, no-battery skip, once-per-node broadcast target, send-failure never throws, cooldown suppression within window + re-alert after expiry via fake timers) plus a DI spec mirroring weather's; an end-to-end case drives a real MeshService over the fake bridge and asserts the alert frame rides channel index 3 with the exact text. `mesh.service.spec.ts` gains a NODEINFO_APP live-update case (stale sync battery refreshed, other fields preserved, unknown-node stub). All pre-existing specs stay green.
+- Tests: new `src/battery/battery.service.spec.ts` (mention hex padding/lowercase, batched message construction incl. multi-node append, name fallbacks and the 190-char ceiling, threshold boundary with default + custom env, no-battery skip, all qualifying nodes merged into exactly one broadcast, send-failure never throws, cooldown suppression within window + re-alert after expiry via fake timers, in-cooldown node excluded from a batch while an out-of-window node still triggers the single message) plus a DI spec mirroring weather's; an end-to-end case drives a real MeshService over the fake bridge and asserts the alert frame rides channel index 3 with the exact text. `mesh.service.spec.ts` gains a NODEINFO_APP live-update case (stale sync battery refreshed, other fields preserved, unknown-node stub). All pre-existing specs stay green.
 
 ## v0.12.8 — 2026-09-25 12:04