e-stepper: step controls after a run, and a slider that counts from 0

[martin-henz]

• Step controls only after a run. Before a run, the tab showed a lone disabled slider handle with its "1" label, and a row of disabled buttons. The slider and the button row now appear once there are steps.
• The slider counts the steps taken. It ran from 1 to the number of states and labelled every ceil(n/10)-th value from 1, so with 174 states the right end read 163 (not 174). It now runs from 0 (the start of the evaluation) to the total number of steps (173 for 174 states), and always labels both ends, with round values in between (a value too close to the last gives way to it).

Tests: no controls before a run, and both after; the slider's range, value and labels, and stepping with the keys; the label values.

🤖 Generated with Claude Code

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[martin-henz]

@codex review

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-09T13:32:59.454930Z	6084ffc	Manual request

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Reviewed commit: 6084ffc3d5

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[chatgpt-codex-connector]

Avoid rendering a zero-width Slider range

When a run produces exactly one state, hasRun is true but this sets both min and max to 0. Blueprint's Slider expects max to be greater than min and calculates positions by dividing over that range, so this case emits validation errors and renders handle/label positions as NaN%. One-state runs are permitted by the runner protocol and are already used throughout this test suite; hide the slider for this case or give it a valid disabled range.

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