frontend: Discard tray MAVLink listeners on destroy

[joaoantoniocardoso]

Summary

• HealthTray HEARTBEAT and GpsTrayMenu GPS listeners are stored with markRaw and discard()ed in beforeDestroy.
• Avoids stacking callbacks on shared MAVLink2Rest endpoints (and deep-observing Endpoint.latestData every frame).

Test plan

• Heartbeat icon and GPS trays still update normally
• Remount / HMR of App tray: listener count does not grow (no duplicate HEARTBEAT handling)
• No regression in armed state / GPS fix display

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Supersedes #4033 (recreated from fork joaoantoniocardoso/BlueOS-docker instead of same-repo head).

[github-actions]

Automated PR Review

0. Summary

• Verdict: LGTM

Fixes listener leaks in the health/GPS tray components: HEARTBEAT and GPS listeners are now stored on the instance and discard()ed in beforeDestroy, and wrapped in markRaw so Vue 2.7's reactivity system does not deep-observe Endpoint.latestData on every incoming MAVLink frame. Directly addresses the AGENTS.md rule "Frontend > 3: Forgetting cleanup — Clear intervals/timeouts in beforeDestroy()", and uses the existing Listener.discard() API (core/frontend/src/libs/MAVLink2Rest/Listener.ts:59, which both clears the interval and removes the listener from the endpoint). markRaw is a valid import in Vue 2.7.14 (per core/frontend/yarn.lock).

No further comments, nice job 👍

Generated by PR Review Bot. This is advisory, a human reviewer must still approve.