a11y(4.1.2): add label prop to Button primitive and enforce accessible names

[rosanusi]

Summary

• Adds a label?: string prop to BaseProps in the Button primitive (src/lib/holocene/button.svelte) rendered as aria-label on both the <a> anchor branch and <button> branch
• Adds a dev-time onMount check that throws (dev) or console.errors (prod) when a button is rendered without any accessible name (no label, aria-label, aria-labelledby, title, slot text, leading/trailing icon, or count badge)
• Updates 7 consumer call-sites that were triggering the defect: Workflows List (per-row Start button + 3 toolbar buttons), Activities List (per-row Start button), Schedules List (toolbar configure-columns button), and Schedule Detail page (refresh button)
• Adds configure-columns i18n key to src/lib/i18n/locales/en/common.ts

Affected files

• src/lib/holocene/button.svelte
• src/lib/i18n/locales/en/common.ts
• src/lib/components/workflow/start-workflow-button.svelte
• src/lib/components/standalone-activities/start-activity-button.svelte
• src/lib/components/workflow/workflows-summary-configurable-table.svelte
• src/lib/pages/schedule-view.svelte
• src/lib/pages/schedules.svelte

Test plan

• Visual regression: all 7 consumer buttons render and function identically; no visible change
• Screen reader (NVDA/VoiceOver): each button announces its label before activation
• Dev-mode enforcement: render a <Button> with no name source — confirm it throws; add label="…" — confirm no throw
• Anchor branch: render <Button href="…"> with no name source — confirm same enforcement fires
• Count badge: render <Button count={3}> — confirm enforcement does not fire (count provides a numeric name)
• pnpm check passes (no new type errors beyond pre-existing $$_$$ slot interop errors on main)

A11y-Audit-Ref: 4.1.2-button-anchor-empty

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Project	Deployment	Actions	Updated (UTC)
holocene	Ready	Preview, Comment	Jul 10, 2026 8:23pm

[ardiewen]

Pushed a revision reworking the approach based on review:

• Dropped the label prop. aria-label is already a typed attribute on Button (its props intersect HTMLButtonAttributes/HTMLAnchorAttributes), so label was redundant — and it reads like it should render visible text. Call sites now pass aria-label directly.
• Dropped the onMount enforcement. It throws in dev for any unlabeled Button (including Storybook/tests), and its hasName check treated a decorative leadingIcon as a name (icon/svg.svelte renders <svg aria-hidden={!title}>, and no title is passed) — so it simultaneously missed real violations (~22 leadingIcon-only buttons) and would have thrown on the equivalent icon-in-slot pattern.
• Fixed 2 icon-only buttons this PR missed (same defect, would have tripped the removed check): activities-summary-configurable-table configure-columns and workflow-current-details refresh.

On enforcement: the repo already has an axe suite (tests/accessibility/) that computes the real accessible name and would catch this correctly — but it isn't gated in CI and has rotted (the page fails to load before axe runs). Repairing + CI-gating it is the right systematic guard, tracked as a follow-up in DT-4255 rather than a bespoke runtime check.