feat: unify gateway heartbeat

docs/configuration.md

@@ -130,7 +130,8 @@ Controls the embedded agent runtime (model/thinking/verbose/timeouts).
     timeoutSeconds: 600,
     mediaMaxMb: 5,
     heartbeat: {
-      every: "30m"
+      every: "30m",
+      target: "last"
     },
     maxConcurrent: 3,
     bash: {
@@ -151,6 +152,9 @@ deprecation fallback.
 - `every`: duration string (`ms`, `s`, `m`, `h`); default unit minutes. Omit or set
   `0m` to disable.
 - `model`: optional override model for heartbeat runs (`provider/model`).
+- `target`: delivery channel (`last`, `whatsapp`, `telegram`, `none`). Default: `last`.
+- `to`: optional recipient override (E.164 for WhatsApp, chat id for Telegram).
+- `prompt`: override the default heartbeat body (`HEARTBEAT`).
 
 `agent.bash` configures background bash defaults:
 - `backgroundMs`: time before auto-background (ms, default 20000)