test(a11y): add static accessibility harness

[luoye520ww]

Problem

The accessibility roadmap needs repeatable checks for high-risk markup, but the repository has no lightweight harness and no DOM test dependency.

Scope

Adds a test-only static markup auditor covering interactive names, form labels, dialog semantics, duplicate IDs, valid aria-labelledby references, and aria-hidden/type-hidden exemptions. It has no runtime or renderer behavior change and adds no dependency.

Non-goals

This is the shared harness only; Workbench, Settings, Write, Connect, and Workflow component remediation remain separate PRs.

Tests

• npm.cmd exec vitest run src/renderer/src/testing/accessibility-harness.test.ts (5 passed)
• npm.cmd run typecheck
• npm.cmd --prefix kun run typecheck
• npm.cmd run lint
• npm.cmd run build
• git diff --check

Review

Completed functional, lifecycle, data integrity, security, cross-platform, compatibility, and scope review. No package smoke is claimed because this is a test-only utility.

Issue

Part of #885

[XingYu-Zhong]

Thank you for introducing the accessibility-test direction. I am closing this PR in favor of #977.

The static regular-expression approach is useful as a prototype, but it cannot reliably model HTML structure and misses important cases such as multiple broken aria-labelledby references, duplicate IDs, hidden subtrees, form-label association, and custom keyboard semantics. The replacement is rebuilt on current develop with a parse5 tree audit and a real production-component test, while explicitly keeping browser/assistive-technology testing out of scope.

Your original contribution is credited in the replacement PR.