[DTM] SOFT-3906 [base] Integration base for the singlebtn design-token proving ground

[pauloiankoski]

Summary

• Lands the Kadence Blocks side of the design-token picker, with the singlebtn Border Radius as the proving ground. Every token-mapped control slot renders as a field-as-trigger input that opens a two-tab popover: Style Library to pick a size token or reset to the inherited default, and Custom for a literal value, unit switch, and slider on one row.
• Keeps all token knowledge in Kadence Blocks. The @kadence/components package stays token-agnostic and only exposes the neutral kadence.components.control.editor / .actions seams, which this branch registers listeners against.
• Narrows the picker to the control's role and prefers the primitive size scale over component-specific semantic radii, and registers that primitive radius scale (None / Small / Medium / Large / Round) as pickable dimension tokens. The values already ship in the baseline, so nothing changes until a step is overridden.
• Derives the singlebtn Border Radius linked/individual mode from the corner values instead of storing a new attribute, so existing buttons open in the right mode and the choice persists across reselecting the block. Per-corner tokens work the same way as linked ones.
• Resolves a bound token to its var(--kb-token--…) reference on both surfaces, so the editor preview and the published page render identically. On the front end this collapses render_measure_output()'s 12 duplicated per-corner branches into one render_measure_side() helper covering the numeric, position-keyword, token-alias, and legacy-spacing-variable cases.
• Pins @kadence/components to feature/design-tokens-module, the branch carrying the merged token-agnostic control seams ([DTM] SOFT-3906 [base] Integration base for token-agnostic control extension seams kadence-components#19), matching how @kadence/helpers is already pinned.

PRs included

• [DTM] SOFT-3906 [1/2]: Pin the kadence-components dependency to the design-tokens dev commit #1172 — Pin the @kadence/components dependency to the design-tokens dev commit
• [DTM] SOFT-3906/SOFT-3995: Blocks-side token seam registration + singlebtn proving ground #1173 — Blocks-side token seam registration and the singlebtn Border Radius proving ground

Test plan

• PHPStan clean
• Full wpunit/acceptance/snapshot suites pass (pre-push CI-equivalent hook)

[linear]

SOFT-3906

[github-actions]

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