Fix smart tariff scale toggle and active styling

[TylonHH]

Motivation

• The chart scale toggle for smart tariff needed to correctly switch between 0–max and min–max modes.
• The active toggle should follow EVCC corporate design and display the green enabled state.
• Price range display should be rounded to whole units for clearer min/max summaries (e.g. 25,6–38,2 → 25–39).
• The change should make the vehicle-status-smartcost UI behave correctly when the switch is toggled.

Description

• Updated assets/js/components/Tariff/SmartTariffBase.vue to use a chart-scale-toggle wrapper and added CSS to style the active toggle with var(--evcc-green).
• Added displayCostRange and formatRangeValue helpers and switched fmtTotalCostRange/fmtActiveCostRange to use the display-aware range so the label reflects zero vs range scale modes.
• Adjusted rounding logic to floor the lower bound and ceil the upper bound and format values in whole units for both currency and CO2 displays.
• Updated assets/js/components/Tariff/TariffChart.vue to normalize the chart heights when scaleMode === 'zero' by treating the minimum as 0 and adjusting the range accordingly.

Testing

• Started the frontend dev server with npm run dev and it launched successfully.
• Ran a Playwright script to load the UI and capture a screenshot (artifacts/smart-tariff-scale.png) which completed successfully.
• No unit or integration test suites (make test / npm run playwright full run) were executed as part of this change.
• Files modified: assets/js/components/Tariff/SmartTariffBase.vue and assets/js/components/Tariff/TariffChart.vue.

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Codex Task