[refactor] /api/health lockdown nit fix needed

[MichaelWheeley]

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• One nit (not blocking): the JSON branch has a redundant persistence: isAuthed ? {...} : { enabled: !!STATS_FILE } ternary inside the ...(isAuthed ? {...} : {}) spread, since the outer condition already guarantees isAuthed. Same with the inner sessions: isAuthed ? ... : ... and pskMqttProxy.activeCallsigns: isAuthed ? ... : .... Could be cleaned up next time you touch the file.

Originally posted by @accius in #940 (review)

please assign to @MichaelWheeley I'm not able to self-assign