…RTBEAT_OK

When a cron agent emits multiple text payloads (narration + tool
summaries) followed by a final HEARTBEAT_OK, the delivery suppression
check `isHeartbeatOnlyResponse` fails because it uses `.every()` —
requiring ALL payloads to be heartbeat tokens. In practice, agents
narrate their work before signaling nothing needs attention.

Fix: check if ANY payload contains HEARTBEAT_OK (`.some()`) while
preserving the media delivery exception (if any payload has media,
always deliver). This matches the semantic intent: HEARTBEAT_OK is
the agent's explicit signal that nothing needs user attention.

Real-world example: heartbeat agent returns 3 payloads:
1. "It's 12:49 AM — quiet hours. Let me run the checks quickly."
2. "Emails: Just 2 calendar invites. Not urgent."
3. "HEARTBEAT_OK"

Previously: all 3 delivered to Telegram. Now: correctly suppressed.

Related: openclaw#32013 (fixed a different HEARTBEAT_OK leak path via system
events in timer.ts)

(cherry picked from commit 2330c71)