feat(settings): select power display targets (#1982)

* feat(settings): select power display targets

Persist a typed powerDisplayTargets preference and apply it to the live Power panel and Cooling Insight charts. Invalid stored values recover to the default CPU, GPU, and package selection while explicit empty selections remain valid.

* fix(settings): address power target review

Serialize rapid power target updates, normalize duplicate command input, and restore in-memory settings when persistence fails. Add regression coverage for each review finding.