Acknowledge design decision on level slider null handling

[Copilot]

Addresses review feedback on #946 regarding the approach to handling null schedule levels in the slider component.

Changes

• No code changes required - the implementation already correctly restricts levelSlider updates to cases where localSchedule.level is not null
• Confirmed design approach: guards prevent slider synchronization instead of using fallback values

Implementation

The level slider menu is gated at three points:

<!-- Menu only renders when level exists -->
<v-menu v-if="localSchedule.level !== null">

// Methods early-return when level is null
cancelLevel() {
  if (this.localSchedule.level == null) return;
  this.levelSlider = this.localSchedule.level;
}

setLevel() {
  if (this.localSchedule.level == null) return;
  this.localSchedule.level = this.levelSlider;
}

This avoids synchronization issues for "manual stop" schedules (where level is null) without needing fallback to vehicle.maximumLevel.

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