[kumo] stabilize button tooltip triggers

[ftzi]

Summary

• Keep one Button tooltip trigger mounted while disabled or loading changes.
• Keep LinkButton tooltip ownership stable while its rendered control changes between an anchor and a disabled button.
• Preserve native disabled-button semantics and title-derived accessible names without nesting tooltips.

Regression coverage

Mounted toggle tests reproduce the old trigger replacement for Button disabled, Button loading, and LinkButton disabled, then assert that the wrapper trigger remains the same DOM node across each transition.

Testing

• vp test run --root packages/kumo --project=unit src/components/button/button.test.tsx
• pnpm run format:check
• pnpm run lint
• pnpm run typecheck
• pnpm run ci:typecheck
• pnpm run test
• pnpm run test:ci
• vp run build:kumo

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• Reviews
  • bonk has reviewed the change
  • automated review not possible because: repository review automation runs after an external contributor opens the pull request
• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because: