fix(popover): Fix popover focus-leave dismissal

[alexwarren]

Stacks fixes to address A11Y-160

Summary

• Close classic s-popover when keyboard focus leaves both the trigger and popover, but only for popover content marked with role="menu".
• Apply the same role-derived focus-leave behavior to Svelte Popover while preserving tooltip, non-menu, and controlled behavior.
• Add regression tests for aria-expanded, menu focus transitions, outside focus, null relatedTarget, controlled close requests, and non-menu popovers staying open.

Why

A11Y-160 reports that dropdown/popover menus remain visually and programmatically expanded after users tab away. This keeps aria-expanded true even though focus has moved outside the trigger/popover pair.

Stacks popovers remain a low-level primitive, so the new dismissal behavior is derived from menu semantics instead of applying to dialogs or generic popover content.

Validation

• npm run test:unit in packages/stacks-classic: 30 passing across Chromium, Firefox, and WebKit.
• npx web-test-runner --config web-test-runner.config.mjs --files src/components/Popover/Popover.test.ts in packages/stacks-svelte: 43 passing.
• npx web-test-runner --config web-test-runner.config.mjs in packages/stacks-svelte: 572 passing.
• npx svelte-check --tsconfig ./tsconfig.json: 0 errors/warnings.
• Package-scoped ESLint and Prettier checks passed.

[netlify]

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[changeset-bot]

🦋 Changeset detected

Latest commit: b63f473

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@stackoverflow/stacks	Minor
@stackoverflow/stacks-svelte	Minor

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[alexwarren]

Replaced by #2298