Open external links in the default browser

[3vcloud]

Summary

• route desktop and Android app links through their native OS browser handlers
• keep only slopterm's loopback origin inside the Android WebView
• cover regular anchors, middle-clicks, and OSC 8 terminal hyperlinks
• add browser-bridge regression coverage for both native shells

Checks

• npm run lint (web)
• npx --no-install oxlint tests/external-links.spec.ts (e2e static lint)
• git diff --check

Builds and compiled tests were not run because this workspace prohibits invoking project builds.