feat(heartbeat): add configurable visibility for heartbeat responses

Add per-channel and per-account heartbeat visibility settings:
- showOk: hide/show HEARTBEAT_OK messages (default: false)
- showAlerts: hide/show alert messages (default: true)
- useIndicator: emit typing indicator events (default: true)

Config precedence: per-account > per-channel > channel-defaults > global

This allows silencing routine heartbeat acks while still surfacing
alerts when something needs attention.

src/infra/heartbeat-events.ts

@@ -1,3 +1,5 @@
+export type HeartbeatIndicatorType = "ok" | "alert" | "error";
+
 export type HeartbeatEventPayload = {
   ts: number;
   status: "sent" | "ok-empty" | "ok-token" | "skipped" | "failed";
@@ -6,8 +8,30 @@ export type HeartbeatEventPayload = {
   durationMs?: number;
   hasMedia?: boolean;
   reason?: string;
+  /** The channel this heartbeat was sent to. */
+  channel?: string;
+  /** Whether the message was silently suppressed (showOk: false). */
+  silent?: boolean;
+  /** Indicator type for UI status display. */
+  indicatorType?: HeartbeatIndicatorType;
 };
 
+export function resolveIndicatorType(
+  status: HeartbeatEventPayload["status"],
+): HeartbeatIndicatorType | undefined {
+  switch (status) {
+    case "ok-empty":
+    case "ok-token":
+      return "ok";
+    case "sent":
+      return "alert";
+    case "failed":
+      return "error";
+    case "skipped":
+      return undefined;
+  }
+}
+
 let lastHeartbeat: HeartbeatEventPayload | null = null;
 const listeners = new Set<(evt: HeartbeatEventPayload) => void>();