frontend: Fix MAVLink2Rest orphan WebSocket reconnects

[joaoantoniocardoso]

Summary

• On intentional close, clear reconnect timeouts and detach onclose so dying sockets cannot resurrect.
• setBaseUrl closes the previous send socket before opening a new one (probe can call setBaseUrl more than once).

Test plan

• Load BlueOS, confirm MAVLink heartbeats / params still work
• Reload / HMR: console should not accumulate reconnecting zombie WS over time
• Vehicle reconnect after autopilot restart still recovers within a few seconds

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Supersedes #4030 (recreated from fork joaoantoniocardoso/BlueOS-docker instead of same-repo head).

[github-actions]

Automated PR Review

0. Summary

• Verdict: LGTM

Fixes orphan WebSocket reconnects in core/frontend/src/libs/MAVLink2Rest/. Both Endpoint and Mavlink2RestManager now track an intentionalClose flag and the pending reconnect setTimeout handle, so intentional closes detach onclose/onmessage, cancel the queued 5 s reconnect, and gate the reconnect branch — preventing the previous behavior where updateUrl()/setBaseUrl() would leave the old socket's onclose alive and reconnecting to the stale URL.

No further comments, nice job 👍

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