fix(a11y): label account QR code button

[Will-thom]

Summary

• Add an accessible label to the account menu QR code icon-only button.
• Add coverage for the QR code button accessible name.
• Add coverage that the app menu trigger buttons expose accessible labels.

Fixes #60292

Tests

• npx vitest run --project nextcloud-ui-legacy core/src/tests/components/AccountMenuProfileEntry.spec.ts core/src/tests/components/AppMenu.spec.ts
• npm run lint
• git diff --check origin/master...HEAD

Validated in a clean Docker container from a fresh nextcloud/server clone using node:24-bookworm.

[susnux]

code looks good, thank you

[szaimen]

🐘

[CarlSchwan]

/compile amend /

[CarlSchwan]

Your commit is missing the DCO

[AndyScherzinger]

/compile

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[AndyScherzinger]

/compile