Fix audit tabs blocked by the Export dropdown (upstream #223)

[jackwalkerlabs]

Upstream: every-app#223

On an individual completed site audit, opening Export prevents clicking Issues / Pages / Performance in a single click. Investigate the actual audit page and fix the event/focus/overlay behavior at its source.

Acceptance:

• Clicking any results tab while Export is open closes the menu and selects that tab with one click.
• Export actions still work. Clicking outside and Escape dismiss the menu; keyboard focus/navigation remain usable.
• Follow existing components and accessibility conventions; keep scope to this interaction.
• Add a focused meaningful interaction regression using the repository's existing test tooling where feasible. Run the relevant tests and full unit suite.
• Record exact checks, outcomes and browser-validation limitations in run output and PR body. Do not require evidence in commit messages.
• Do not use live paid APIs or modify deployment credentials. If browser setup prevents reproducing the real page, state that clearly rather than claiming a browser pass.

[jackwalkerlabs]

FactoryChief completed this issue in #9. The exact pushed SHA passed an isolated verification container. Human review is required before merge.