DEV-2104: make docs examples bucket-aware

[demtario]

Summary

Task: https://app.clickup.com/t/9015210959/DEV-2104

• resolve docs-example buckets from the selected Handsontable version and hide unavailable docs entries
• reload clean docs workspaces across buckets while preserving edited files with a compatibility warning
• isolate manifest/entry caches by bucket and add bucket-layout and version-switch regressions

Test plan

• pnpm test
• pnpm --filter @handsontable/demo-authoring run typecheck
• pnpm --filter @handsontable/demo-authoring build
• pnpm e2e -- e2e/docs-examples.spec.ts (10 passed, 1 live test skipped by design)
• manually switched a committed Accessibility example from 18.0 to next and confirmed the rendered bucket content changed

Base dependency

The generated 18.0 and next artifacts are already merged into feature/DEV-2099_Versioned-docs-examples via PR #65.

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Note

Medium Risk
Touches core playground load/version-switch flows and async race handling; wrong bucket logic could show mismatched API examples, but behavior is guarded with explicit errors, no silent fallback to next, and broad E2E coverage.

Overview
Documentation examples in the playground are now loaded from version-specific buckets (major.minor or next when the selected version matches npm’s dist-tags.next), instead of a single flat catalog.

Authoring behavior: After versions resolve from the API, the app derives a bucket, fetches that bucket’s manifest (as the “does this version have docs?” check), and drives the cascader from those entries only. Changing Handsontable version on a clean docs workspace reloads the same ?docs= path from the new bucket; with unsaved edits, source is kept, dependencies/CSS are re-pinned, and a compatibility warning is shown. Missing buckets or paths block the preview (blank iframe) with recoverable errors rather than falling back to starters or the wrong API.

Supporting changes: docs-catalog and caches are keyed by bucket; deriveDocsBucketCandidate is shared from demo-runtime; pipeline smoke and Playwright tests cover bucket layout and version-switch regressions.

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