test(inspector): add keyboard-only accessibility coverage #25

Context

The inspector is usable with pointer input, but the stable-release gate needs a keyboard-only regression path for opening, navigating, and closing it.

Scope

• Add a Playwright scenario that opens the inspector without pointer-only shortcuts.
• Exercise the Why, Values, State, Network, and Timeline navigation using keyboard input.
• Verify visible focus, the active tab state, and a predictable focus destination after closing.
• Keep the fixture TypeScript/TSX-only and reuse the React 19 diagnostic lab.
• Fix any inspector semantics exposed by the test rather than weakening the assertions.

Acceptance

• The new test fails if a keyboard user cannot reach or identify the active inspector view.
• Existing pointer selection and direct reselection remain green.
• pnpm check passes.