Scale tariff chart bars to observed min/max and clamp heights

[TylonHH]

Motivation

• Improve visual contrast by scaling tariff/price bars to the actual observed minimum and maximum instead of always from zero to max.
• Avoid misleading tall bars when values are tightly clustered or all above zero.
• Provide a sensible, neutral fallback for empty or constant data ranges.

Description

• Compute valueInfo from observed slot values using Number.NEGATIVE_INFINITY/Number.POSITIVE_INFINITY and return { min: 0, range: 0 } when no values are present.
• Update valueStyle to return a neutral 50% height when the computed range is 0 or when the input is undefined/NaN.
• Normalize bar heights with (val - min) / range, clamp them to 0..1, and return the percentage height as ${clamped * 100}%.

Testing

• Started the dev server with npm run dev, which launched and served the app successfully.
• Ran a Playwright script to load the page and capture a screenshot, producing artifacts/tariff-chart-updated.png.
• No unit or integration test suites were executed as part of this change.

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Codex Task