Setup web+ap handler with the PWA

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There should be an easy way to open the app from a link.

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It would be cool if this supported [`web+ap`](https://fedilinks.org/6) using [the PWA](https://developer.mozilla.org/en-US/docs/Web/Manifest/protocol_handlers). This is probably the cleanest approach.

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The most widely supported approach to opening the user's preferred fedi app is using `web+ap`, as it is supported in the feditext and tokodon native clients. While there are other ways a webapp can solve this problem (implementing webfinger and taking advantage of the remote interactions dialog, for example), they're not really viable for this app (because it uses static pages).

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https://github.com/cheeaun/phanpy/assets/1779619/acddf6e0-c1e2-4e92-bd69-339b66a622bf