Add YAML example to every step reference entry

[lg345]

What changed

Every step entry in the Step reference now carries a short YAML snippet
showing a typical invocation. Previously only a handful had examples.

Covers all four category pages (loading & filtering, detector & spatial,
binning, spectra & reductions), plus the combine_runs reduction.

Test

mkdocs build renders all pages with no broken-link warnings.

[Copilot]

Pull request overview

This PR updates the Step Reference documentation to consistently include a short YAML usage snippet for each step/reduction entry, improving discoverability and “copy/paste” usability across the docs.

Changes:

• Added YAML invocation examples for step entries across all four step-category pages.
• Added a YAML example for the combine_runs cross-run reduction under the reduction: section.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docs/steps/loading_filtering.md	Adds YAML snippets for loading and shot-selection steps (e.g., loading keys/detectors, mask construction, filtering).
docs/steps/detector.md	Adds YAML snippets for detector correction/geometry/reduction steps (e.g., patching pixels, ROI, spatial/shot reductions).
docs/steps/binning.md	Adds YAML snippets for axis/bin-index builders and binned reductions (temporal/energy/2D).
docs/steps/spectra.md	Adds YAML snippets for spectra utilities and the combine_runs reduction under reduction:.

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