Fix #6856
Fix #6951

Fix #10116

* Change remote interaction dialog to use specific actions

Instead of just "interact", use different strings based on whether
it's a reply, reblog or favourite. Add explanation why the step
is necessary in the first place

* Remove obsolete strings

* Add follow button to detailed status, add gradient to mask bio cut-off

* In landing strip, show sign up link even if closed (different href)

Point to joinmastodon.org

* Make embeds cacheable by reverse proxy

* Make follow button on embeds open remote follow modal

Instead of web+mastodon://, also, turn the button blue, and add a
sign up prompt to the remote follow modal

* Add coverage for remote_follow#new

* Fix reference to authorize_follows/card partial