fix(frontend): give the icon links and small dialogs accessible names

[JuliusHenke]

What

Two accessibility gaps, found by reviewing the frontend against Safari's built-in accessibility audit (testForLinkLabels, testDialogsForLabels):

• Icon-only links: the GitHub, Twitter and mail links in the About dialog contained only an aria-hidden MUI icon, so a screen reader announced them as just "link". ExternalLink gets an optional ariaLabel, and the three links now have TorMap on GitHub, TorMap on Twitter and Email TorMap.
• Dialogs on small screens: the full screen dialogs for settings, families and relay details show a Typography instead of DialogTitle, so they had role="dialog" without a name. They now have aria-label ("Settings", "Families", "Relay details" / "Relays"). The large-screen dialogs use DialogTitle and were already labelled.

MUI applies aria-label on a Dialog to its root element, not to the role="dialog" paper, so it is set through slotProps.paper. A first attempt on the root was caught by the new tests.

Verification

tsc, eslint and yarn test:run pass (281 tests, 6 new): every dialog is found by role with its accessible name on both screen sizes, and the three links are found by name with the right href.

Not verified: I could not run Safari's audit itself (the WebInspectorAudit API only exists inside Safari). If the audit still reports something, the failing test name and element would tell what is left.

Dependencies / deployment

None.

🤖 Generated with Claude Code

[github-actions]

Visit the preview URL for this PR (updated for commit c43fec4):

https://tormap-36f44--pr612-fix-frontend-a11y-di-nz16lk4f.web.app

_{(expires Wed, 11 Nov 2026 20:38:38 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

_{Sign: 0c1f71965de18e60b0e686b0d0356977fec090dc}