stepper: clicking the step slider goes to the step clicked

[martin-henz]

Same fix as the e-stepper's (#165). Blueprint's slider measures its track once, when it mounts, and converts a click to a step with that width; if the tab is resized afterwards, a click lands on the wrong step (slightly, in the stepper). The slider is now keyed by the tab's width, so it measures again after a resize.

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🦋 Changeset detected

Latest commit: b4db4a0

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[martin-henz]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: b4db4a0ad5

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-11T01:58:47.605632Z	b4db4a0	Manual request

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