Add Tooltip component and state-rendering tests (loading/empty/error/success)

[harshaaaaw]

What

Adds a Tooltip component for StableRoute-Org/Stableroute-frontend and tests asserting it renders correctly for the four mutually-exclusive states: loading, empty, error, and success.

How to use

<Tooltip status="success" message="Done">
  <button>Hover me</button>
</Tooltip>

How it works

The component renders its trigger children plus a role="status" surface driven by a status prop. States are mutually exclusive; the status text is exposed via aria-live="polite" for assistive tech.

Testing

• 7 new tests covering all four states, mutual exclusivity, and a11y.
• Full suite: 1247 passed, 72 suites. npm run lint clean.

Closes #685