feat(landing): point Open app at get.wingover.app for everyone

[aeharding]

Alex's call: with the app live and Universal Links working, the nav button should just go to https://get.wingover.app.

• Open app now links there statically, for every platform.
• The iOS UA-sniffing rewrite script is deleted (net -16 lines): get.wingover.app is already the one place that routes by platform (installed iOS app opens via Universal Link; iOS without it gets the App Store; everyone else lands on /logbook). The tap-from-landing path is the flow device-tested in July; this PR only extends the same href to non-iOS visitors, whose fallback is the same /logbook they got before, one redirect hop later.
• Tradeoff accepted: iOS visitors without the app see "Open app" but land on the App Store. The Smart App Banner already carries the explicit install affordance, so no script survives just to relabel a button.
• The hero's "Open your logbook in the browser" link stays /logbook: it says browser and means it.

Gates: tsc, eslint --max-warnings 0, format:check, check:css, vitest, playwright 105 passed / 10 skipped (exit code checked directly).

Merge burns a TestFlight build (public/** is in testflight.yml paths). Deploys to beta on merge; prod rides the next release tag.