#10677: fix(heartbeat): mirror outbound messages to session transcript

## Problem Heartbeat-initiated outbound messages were not being mirrored back into the session transcript, causing context confusion when users replied to heartbeat messages. The agent had no memory of what it sent. ### Reproduction scenario: 1. Heartbeat triggers agent to send a proactive message (e.g., "was machst du grad?") 2. User receives the message via Telegram/etc 3. User replies to that message 4. Agent has no context about the original message it sent 5. Agent is confused about what the user is replying to ## Fix This adds the `mirror` parameter to the `deliverOutboundPayloads` call in `runHeartbeatOnce`, matching the pattern established by #1031 for other delivery paths (routeReply, message tool, gateway send API). The `mirror` parameter was already implemented and working for other delivery paths — heartbeat just wasn't using it. ## Changes - Added `mirror` parameter to the main heartbeat delivery call - Only mirrors when there's actual content to send (`shouldSkipMain` is false) - Passes `sessionKey`, `agentId`, `text`, and `mediaUrls` for proper transcript recording <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> - Updates the heartbeat delivery path to pass `mirror` options into `deliverOutboundPayloads`, so outbound heartbeat messages are also appended to the session transcript. - Mirrors `sessionKey`/`agentId` plus the heartbeat’s normalized text and media URLs, aligning heartbeat behavior with other outbound delivery paths. - Avoids mirroring when the main heartbeat message is skipped (`shouldSkipMain`). <h3>Confidence Score: 4/5</h3> - This PR is likely safe to merge, but has a functional gap for heartbeats that deliver reasoning-only messages. - Change is small and follows existing mirroring mechanism, but the mirroring payload does not reflect all delivered outbound heartbeat content when `includeReasoning` is enabled, so the stated context-confusion bug can still occur in that mode. - src/infra/heartbeat-runner.ts <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->