feat(Thermals): highlight series on mouse hover

[pedrolamas]

Enables series highlighting on the thermal chart by hovering the series directly on the chart or hovering the item in the thermal entries list.

Screen Capture

Video.mp4

Resolves #1536

[Copilot]

Pull request overview

Adds mouse-hover-driven series emphasis to the thermal chart. Hovering a row in the temperature table or a line on the chart highlights the corresponding series (and its target/power/speed siblings) while fading others, using ECharts' built-in focus: 'series' and highlight/downplay actions.

Changes:

• Switch per-series emphasis from manual lineStyle.width to focus: 'series' in ThermalChart, and expose highlightSeries(key) / downplaySeries() that dispatch the matching ECharts actions for the base key plus its #target/#power/#speed siblings.
• Emit highlightChartSeries / downplayChartSeries from heater/fan/sensor table rows on mouseenter/mouseleave in TemperatureTargets.
• Forward those events from TemperatureCard to the ThermalChart ref, guarded by chartVisible (mirroring the existing updateChartSelectedLegends forwarder).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/components/widgets/thermals/ThermalChart.vue	Use focus: 'series' for emphasis; add imperative highlightSeries/downplaySeries methods that dispatch ECharts highlight/downplay including related sub-series.
src/components/widgets/thermals/TemperatureTargets.vue	Add mouseenter/mouseleave handlers on heater, fan, and sensor rows that emit highlight/downplay events with the item key.
src/components/widgets/thermals/TemperatureCard.vue	Bridge child hover events to the thermal chart ref, gated on chartVisible.